Multilayer integral geogrids having a cellular layer structure, and methods of making and using same

ABSTRACT

A multilayer integral geogrid, including one or more cellular layers, has a plurality of oriented multilayer strands interconnected by partially oriented multilayer junctions with an array of openings therein. The multilayer integral geogrid having one or more cellular layers is produced from a coextruded or laminated multilayer polymer starting sheet. The integral geogrid has a multilayer construction, with at least one outer layer thereof having the cellular structure. By virtue of the cellular layer structure, the multilayer integral geogrid provides for increased layer vertical compressibility under load, resulting in enhanced material properties that provide performance benefits to use of the multilayer integral geogrid to stabilize and strengthen soil, aggregates, or other particulate materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit of priority toU.S. patent application Ser. No. 17/355,843 entitled “Multi-AxialIntegral Geogrid and Methods of Making and Using Same” filed Jun. 23,2021, and International Patent Application No. PCT/US2021/038863entitled “Multi-Axial Integral Geogrid and Methods of Making and UsingSame” filed Jun. 24, 2021; both applications which further are relatedto and claim priority to U.S. Provisional Application for Patent No.63/043,627 entitled “Multi-Axial Integral Geogrid and Methods of Makingand Using Same” filed Jun. 24, 2020, U.S. Provisional Application forPatent No. 63/154,209 entitled “Multilayer Integral Geogrids Having aCellular Layer Structure, and Methods of Making and Using Same” filedFeb. 26, 2021, and U.S. Provisional Application for Patent No.63/154,588 entitled “Horizontal Mechanically Stabilizing Geogrid withImproved Geotechnical Interaction” filed Feb. 26, 2021. This applicationis also related to a patent application entitled “HorizontalMechanically Stabilizing Geogrid with Improved Geotechnical Interaction”being filed concurrently herewith. The disclosures of said applicationsare incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to integral geogrids and otheroriented grids used for structural or construction reinforcement andstabilization, and other geotechnical purposes. More particularly, thepresent invention relates to such integral geogrids having a multilayerconstruction, including one or more layers having a cellular structure,that provides enhanced vertical compressibility and enhanced frictionalcharacteristics of the integral geogrid. The present invention alsorelates to such integral geogrids having the ability to engage with andstabilize a greater variety and range of quality of aggregates, and, aswell as other desirable characteristics as disclosed herein. The presentinvention also relates to soil constructions incorporating the integralgeogrid of the present invention which are characterized by enhancedengineering behavior and properties, such as, for example, density,stiffness, strength, and ductility.

This invention also relates to the method of producing such multilayerintegral geogrids having one or more cellular layers. Lastly, thepresent invention relates to the use of such multilayer integralgeogrids for soil and particulate reinforcement and stabilization, andmethods of such reinforcement and stabilization.

For the purpose of this invention, the term “integral geogrid” isintended to include integral geogrids and other integral grid structuresmade by orienting (i.e., stretching) a polymeric starting material inthe form of a sheet or a sheet-like shape of a requisite thickness andhaving holes or depressions made or formed therein.

2. Description of Related Art

Polymeric integral grid structures having mesh openings defined byvarious geometric patterns of substantially parallel, oriented strandsand junctions therebetween, such as integral geogrids, have beenmanufactured and sold for over 35 years. Such grids are manufactured byextruding and forming an integrally cast starting sheet having aspecified pattern of holes or depressions which is followed by thecontrolled uniaxial or biaxial stretching and orientation of the sheetinto highly oriented strands (also sometimes hereinafter referred to asribs) and partially oriented junctions defining mesh openings formed bythe holes or depressions. Such stretching and orienting of the sheet ineither a uniaxial or a biaxial direction develops strand tensilestrength and modulus. These integral oriented polymer grid structurescan be used for retaining or stabilizing particulate material of anysuitable form, such as soil, earth, sand, clay, gravel, etc. and in anysuitable location, such as on the side of a road or other cutting orembankment, beneath a road surface, runway surface, etc.

Various shapes and patterns of holes have been experimented with toachieve higher levels of strength to weight ratio, or to achieve fasterprocessing speeds during the manufacturing process. Orientation isaccomplished under controlled temperatures and strain rates. Some of thevariables in this process include draw ratio, molecular weight,molecular weight distribution, and degree of branching or cross linkingof the polymer.

The manufacture and use of such integral geogrids and other integralgrid structures can be accomplished by well-known techniques. Asdescribed in detail in U.S. Pat. No. 4,374,798 to Mercer, U.S. Pat. No.4,590,029 to Mercer, U.S. Pat. No. 4,743,486 to Mercer and Martin, U.S.Pat. No. 4,756,946 to Mercer, and U.S. Pat. No. 5,419,659 to Mercer, astarting polymeric sheet material is first extruded and then punched toform the requisite defined pattern of holes or depressions. The integralgeogrid is then formed by the requisite stretching and orienting of thepunched sheet material.

Such integral geogrids, both uniaxial integral geogrids and biaxialintegral geogrids (collectively “integral geogrids,” or separately“uniaxial integral geogrid(s)” or “biaxial integral geogrid(s)”) wereinvented by the aforementioned Mercer in the late 1970s and have been atremendous commercial success over the past 35 years, totallyrevolutionizing the technology of reinforcing soils, roadwayunderpavements and other civil engineering structures made from granularor particulate materials.

Mercer discovered that by starting with a relatively thick,substantially uniplanar polymer starting sheet, preferably on the orderof 1.5 mm (0.059055 inch) to 4.0 mm (0.15748 inch) thick, having apattern of holes or depressions whose centers lie on a notionalsubstantially square or rectangular grid of rows and columns, andstretching the starting sheet either unilaterally or biaxially so thatthe orientation of the strands extends into the junctions, a totally newsubstantially uniplanar integral geogrid could be formed. As describedby Mercer, “uniplanar” means that all zones of the sheet-like materialare symmetrical about the median plane of the sheet-like material.

In U.S. Pat. No. 3,252,181 to Hureau, U.S. Pat. No. 3,317,951 to Hureau,U.S. Pat. No. 3,496,965 to Hureau, U.S. Pat. No. 4,470,942 to Beretta,U.S. Pat. No. 4,808,358 to Beretta and U.S. Pat. No. 5,053,264 toBeretta, the starting material with the requisite pattern of holes ordepressions is formed in conjunction with a cylindrical polymerextrusion and substantial uniplanarity is achieved by passing theextrusion over an expanding mandrel. The expanded cylinder is then slitlongitudinally to produce a flat substantially uniplanar starting sheet.

Another integral geogrid is described in U.S. Pat. No. 7,001,112 toWalsh (hereinafter the “Walsh '112 patent”), assigned to TensarInternational Limited, an associated company of the assignee of theinstant application for patent, Tensar International Corporation, Inc.(hereinafter “Tensar”) of Atlanta, Ga. The Walsh '112 patent disclosesoriented polymer integral geogrids including a biaxially stretchedintegral geogrid in which oriented strands form triangular mesh openingswith a partially oriented junction at each corner, and with six highlyoriented strands meeting at each junction (hereinafter sometimesreferred to herein as “triaxial integral geogrid”). The triaxialintegral geogrids of the Walsh '112 patent have been commercialized byTensar to substantial success.

Still another integral geogrid is disclosed in U.S. Pat. No. 9,556,580to Walsh, U.S. Pat. No. 10,024,002 to Walsh, and U.S. Pat. No.10,501,896 to Walsh, all of which are assigned to Tensar TechnologiesLimited, another associated company of the assignee of the instantapplication for patent. The aforementioned Walsh U.S. Pat. Nos.9,556,580, 10,024,002, and 10,501,896 disclose an integral geogridhaving what is known to one skilled in the art as a high aspect ratio,i.e., a ratio of the thickness or height of the strand cross section tothe width of the strand cross section, that is greater than 1.0. Whileit has been shown that the performance of multiaxial integral geogridscan be improved by using a geogrid structure that has ribs with anaspect ratio greater than 1.0, the increase in aspect ratio comes withincreases in the overall amount of polymer required, thus increasing theweight and cost of the geogrid.

Traditionally, the polymeric materials used in the production ofintegral geogrids have been high molecular weight homopolymer orcopolymer polypropylene, and high density, high molecular weightpolyethylene. Various additives, such as ultraviolet light inhibitors,carbon black, processing aids, etc., are added to these polymers toachieve desired effects in the finished product and/or manufacturingefficiency.

And, also traditionally, the starting material for production of suchintegral geogrids has typically been a substantially uniplanar sheetthat has a monolayer construction, i.e., a homogeneous single layer of apolymeric material.

While an integral geogrid produced from the above-described conventionalstarting materials exhibits generally satisfactory properties, it isstructurally and economically advantageous to produce integral geogridswhich when incorporated in soil constructions provide a relativelyhigher degree of stiffness suitable for the demands of certainapplications such as geosynthetic reinforcement or having otherproperties desirable for a particular geosynthetic application.

Thus, a need has existed for a starting material not only that issuitable for the process constraints associated with the production ofintegral geogrids, but also that once the integral geogrid has beenproduced and is in service, provides a higher degree of soilconstruction stiffness than that associated with conventional geogridstarting materials, or provides other desirable properties not availablewith current monolayer integral geogrids, such as, for example, density,strength, and ductility.

Furthermore, while an integral geogrid produced from the above-describedconventional starting materials and in conventional configurations mayexhibit generally satisfactory properties, it is structurally andeconomically advantageous to produce an integral geogrid having astructure and geometry with the ability to engage with and stabilize agreater variety and range of quality of aggregates that is suitable forthe demands of particular service applications, such as geosyntheticreinforcement or having other properties desirable for particulargeosynthetic applications.

It is intended that the present invention be applicable to all integralgrids regardless of the method of starting sheet formation or the methodof orienting the starting material into the integral geogrid or gridstructure. The subject matter of the foregoing U.S. Pat. Nos. 3,252,181,3,317,951, 3,496,965, 4,470,942, 4,808,358, 5,053,264, 7,001,112,9,556,580, 10,024,002, and 10,501,896, is expressly incorporated intothis application by reference as if the disclosures were set forthherein in their entireties. These patents are cited as beingillustrative, and are not considered to be inclusive, or to excludeother techniques known in the art for the production of integral polymergrid materials.

Despite the functional characteristics available with current monolayerintegral geogrids, there are performance improvements that have yet tobe attained over prior art integral geogrids. One such enhancement isdisclosed in U.S. application Ser. No. 15/766,960 (hereinafter “the '960application”; published as U.S. Patent Application Publication No.2018/0298582 A1), also assigned to Tensar International Limited. The'960 application discloses various embodiments for coextruded multilayerpolymer sheets as the starting material for fabrication of integralgeogrids. By virtue of the coextruded multilayer starting materialconstruction, the coextruded multilayer sheet components, afterextrusion and orientation, produce integral geogrids having enhancedmaterial properties that provide performance benefits in soilgeosynthetic reinforcement.

One of the embodiments disclosed in the '960 application is athree-layer integral geogrid produced from a coextruded three-layerstarting sheet in which the middle layer of the oriented integralgeogrid has an expanded or “foamed” structure. According to the '960application, the only advantages of the expanded or foamed multilayerstructure are reduced raw material cost and reduced geogrid weight and“may include desirable physical and chemical properties of the foamedlayer per se.” No other benefits associated with the expanded or foamedmultilayer structure are disclosed. The subject matter of the '960application is expressly incorporated into this application by referenceas if the disclosure was set forth herein in its entirety.

To date, current integral geogrid products manufactured from currentproduction/process technologies can generate multiaxial geogrid productswith desirable attributes and features; however, currentprocess/production technology does not allow for changes in materialtype within the cross section of the overall geogrid. As a result, toenhance the desired physical, mechanical, and geometrical propertiesthat improve performance, significant increases in the amount of polymeris required.

Additionally, current process/production technology limits the abilityto increase or enhance certain parameters that drive performance, whileconcurrently controlling or not changing other parameters that, ifchanged, reduce performance.

Furthermore, current process/production technology does not address theuse of differing polymer materials in different portions of the geogridstructure as a means of maximizing performance.

Accordingly, a need exists for integral geogrids that allow for better“initial compatibility” between the aggregate and the geogrid, thusmaximizing the aggregate density after compaction is complete, andthereby minimizing any possible remaining aggregate movement orrepositioning that would normally occur after compaction and uponinitial phases of “in service” loadings. Even more specifically, a needexists for an integral geogrid having the aforementioned attributes byproviding for increased layer compressibility under load. The term“initial compatibility” is used herein to mean a maximizing of theaggregate density after compaction is complete to thereby minimizepotential movement or positioning of the aggregate that would normallyoccur after compaction and upon initial phases of the “in service”loadings.

SUMMARY OF THE INVENTION

The object of the instant invention, therefore, is to deliver improvedfunctional performance from multiaxial integral geogrids by enhancingcertain physical, mechanical, and geometrical properties of themultiaxial integral geogrid structure that improves functionalperformance, such as by modifying and/or incorporating other newphysical, mechanical, and geometrical properties. By careful physicalpositioning and manipulating of the amount of different polymericmaterials that have the desired mechanical and physical properties inspecific locations of integral geogrid structures, and by optimizing allother physical parameters of the geogrid structure, significantperformance improvements can be achieved.

Another object of the instant invention is to provide a multilayerintegral geogrid in which layers thereof are modified to reduce theamount of polymer required by converting the polymer in those layersfrom a solid, i.e., continuous, structure to a cellular structure, i.e.,a structure having dispersed therein a plurality of voids, cavities,pores, fissures, bubbles, holes, or other types of openings, i.e.,cellular openings, produced according to the methods described herein.

More specifically, subsequent to the filing of the '960 application, ithas been surprisingly discovered that improved initial compatibilitybetween the aggregate and layers of the multilayer integral geogridhaving the cellular structure can be achieved if certain parameters forthe layers with the cellular structure are included in the geogrid, asdisclosed herein. These parameters include the following:

-   -   1. the minimum rib thickness or height of the multilayer        integral geogrid having one or more cellular layers in        accordance with the present invention is preferably from about        0.5 mm to about 6 mm, and more preferably from about 1.15 mm to        about 4 mm.    -   2. the aspect ratio of the ribs of the multilayer integral        geogrid having one or more cellular layers in accordance with        the present invention is preferably from about 0.75 to about        3.0, and more preferably from about 1 to about 2.    -   3. the initial height or thickness of the one or more cellular        layers at their thinnest height (likely the midpoint of the        strands or ribs) after stretching is from about 0.1 mm to about        4 mm, and more preferably from about 0.5 to about 3 mm;    -   4. the cellular openings of the one or more cellular layers        comprise at least 20% by volume of the one or more cellular        layers, and preferably from about 30% to about 50%;    -   5. the one or more cellular layers have a minimum “crushability”        or height reduction under load of at least 20% and preferably        from about 30% to about 50%; and    -   6. the one or more cellular layers have a height or thickness        that is at least 10% of the overall height of the final integral        geogrid, and preferably from about 20% to about 35%.

By including the above physical properties in the multilayer integralgeogrid having the one or more cellular layers in accordance with thepresent invention, the initial compatibility between the aggregate andthe geogrid is improved after compaction is complete. And, by improvingthe initial compatibility, any possible remaining aggregate movement orrepositioning that would normally occur during and after compaction inthe initial phases of “in service” loading is reduced. Thus, the roadwayor other transporting surface, or aggregate or soil layer, is betterstabilized and improved at the time of construction, and any deformationor movements that occur during in service use or loadings is reduced.

More specifically, by virtue of using the multilayer integral geogridhaving the one or more cellular layers, the instant invention providesfor improved micro-interaction as the layers of compressible polymerserve to nest aggregate particles and facilitate and maintain maximumproperties of the aggregate.

In addition, by carefully modifying the polymer to reduce the densityand/or volume of polymer used in one or more of the layers of theextruded sheet used to manufacture the multilayer integral geogrid, anintegral geogrid structure can be created that has equivalent physicaldimensions to traditional integral geogrids, but with less polymermaterial use and thus less cost.

Accordingly, to attain the aforementioned objects, the present inventionis directed to integral geogrids having a multilayer construction, withat least one layer thereof having a cellular structure. These multilayergeogrids are often referred to herein as integral geogrids having atleast one layer thereof with a cellular structure, or, more simply, a“multilayer integral geogrid having one or more cellular layers” or“multilayer integral geogrids having one or more cellular layers.” Byvirtue of the multilayer integral geogrids having one or more cellularlayers, the multilayer integral geogrids of the present inventionprovide for increased layer compressibility under load, and otherdesirable characteristics.

More specifically, the layer or layers having the cellular structurecontain a distribution of a plurality of cellular openings, i.e., voids,cavities, pores, fissures, bubbles, holes, or other types of openingstherein. The cellular structure may be associated with a foamedconstruction of the layer, or may be associated with a particulatefiller that is distributed throughout the layer, or may be any othermethod of creating cellular openings in the cellular layer.

And, for an embodiment of the present invention having three or morelayers, the compressible layers thereof having a cellular structure arepreferably positioned at least as the two outer (or exterior or “cap”)layers of the multilayer integral geogrid. There are uniquegeo-mechanical advantages to having the two outer layers becompressible. One important advantage: the compressible outer layersallow for the aggregate to not only strike through the apertures and beconfined in the apertures, but also to become embedded in the outerlayers of the integral geogrid surface, thereby creating what issometimes referred to herein as a “crush-fit” phenomenon. With theaggregate being “crush-fit” into the surface of the cellular outerlayers of the integral geogrid, the integral geogrid is able to provideenhanced lateral restraint of the aggregate under loading by resistingmovement of the aggregate via enhanced frictional characteristics of thesurface of the cellular outer layers, and by the binding action thatoccurs by the aggregate particles partially crushing into the surface ofthe cellular outer layers.

Because the crushable character of the cellular outer layers providesboth plastic and elastic deformation, the aggregate pushes into theouter layer and binds into the surface thereof. At the same time, thesurface of the outer layer pushes back, enhancing the bond and“crush-fit” between the aggregate and the multilayer integral geogrid.And, according to certain embodiments of the invention, the crushablecharacter of the cellular outer layers may have the potential to createa chemical bond with the surrounding soils. By combining an improvedgeometry as described herein with an enhanced engineered outer layerstructure, the multilayer integral geogrid according to the presentinvention provides for enhanced performance via improved confinement andlateral restraint of the aggregate.

A primary attribute of the multilayer integral geogrid according to thepresent invention is the compressibility or crushability of the cellularlayer or layers. For example, in the above-described three-layerembodiment, the compressibility of the two outer cellular layers isimportant to allowing the aggregate to bed into the surface of theintegral geogrid. Ideally, each compressible layer is durable enough totolerate the process of being embedded in particulate matter (i.e., inthat it will resist delamination from other layers, or shred), and willcompress at least about 20% under load. Additionally, the compressiblelayer will rebound by at least about 85%. A fundamental concept of thepresent invention is that the cellular layer be compressible enough toaccommodate the aggregate during embedding, but also then to “rebound,”as the compressible cellular layer pushes back against the aggregate to“bind” the multilayer integral geogrid in place. The crushing and therebound are believed to improve performance via frictional and bindingattributes that result in improved lateral restraint of the aggregate.

Furthermore, the construction of the multilayer integral geogrids havingone or more cellular layers may include layers that are coextruded, orlayers that are laminated. The creation of the cellular openings in thelayer with the cellular structure may occur during extrusion/laminationor stretching/orientation, or both.

And, the resulting multilayer integral geogrids having a layer or layerswith a cellular structure and having the plurality of orientedmultilayer strands interconnected by the partially oriented multilayerjunctions and having an array of openings therebetween may be configuredin any of a variety of repeating geometric patterns, such as describedherein.

According to the present invention, a starting material for makingmultilayer integral geogrids having one or more cellular layers includesa multilayer polymer starting sheet having holes or depressions thereinthat provide an array of shaped openings when the starting material isbiaxially stretched. The multilayer polymer starting sheet includes oneor more layers that are capable of forming the cellular structure. Twopreferred embodiments are described in detail herein. In the firstpreferred embodiment according to the present invention, the layercapable of forming the cellular structure includes a foaming agent whichupon extrusion of the layer and/or stretching/orientation of thestarting sheet forms the cellular layer as part of the final multilayergeogrid (hereinafter sometimes “the foamed embodiment”).

In the second preferred embodiment according to the present invention,the layer capable of forming the cellular structure includes aparticulate filler dispersed in the layer which uponstretching/orientation of the starting sheet creates the cellularstructure in the layer as part of the final multilayer geogrid(hereinafter sometimes “the filler embodiment”). According to preferredembodiments, the layers of the multilayer polymer starting sheet may becoextruded, or may be laminated to one another.

In addition to the two preferred embodiments described in detail herein,the present invention also contemplates other methods of creating thecellular openings for the cellular layer or layers which may be devisedby those skilled in the art, such as gas injection or the like, so longas the cellular openings that are in the cellular layer comport with theparameters set forth herein.

According to specific embodiments of the present invention, themultilayer integral geogrids having one or more cellular layers includea plurality of oriented multilayer strands interconnected by partiallyoriented multilayer oriented junctions and having an array of openingstherebetween. According to one embodiment, a three-layer integralgeogrid has a non-cellular layer interposed between two outer layerswith cellular structures. According to another embodiment, a multilayerintegral geogrid has a repeating pattern of a non-cellular layerinterposed between two layers with cellular structures. According tostill another embodiment, the multilayer integral geogrid has anon-cellular layer associated with an adjacent layer having a cellularstructure.

According to one embodiment, the multilayer integral geogrid having oneor more cellular layers is a rectangular geogrid having a repeatinggeometric pattern of partially oriented junctions interconnectingoriented strands which define rectangular openings. According to anotherembodiment, the multilayer integral geogrid having one or more cellularlayers is a triaxial geogrid having a repeating hexagonal geometricpattern of partially oriented junctions interconnecting oriented strandswhich define triangular openings. And, according to yet anotherembodiment, the multilayer integral geogrid having one or more cellularlayers is a geogrid having a repeating geometric pattern of partiallyoriented junctions interconnecting oriented strands which form outerhexagons, each of which outer hexagons surrounds and supports six innerinterconnected oriented strands formed into the shape of an innerhexagon and defining a smaller hexagonal opening, referred to herein asa “repeating floating hexagon within a hexagon pattern.” This embodimentof the present invention that has the “repeating floating hexagon withina hexagon pattern” is also sometimes referred to herein as the“hexagonal” embodiment.

According to still another embodiment of the present invention, a soilconstruction includes a mass of particulate material strengthened andstabilized by embedding therein a multilayer integral geogrid having oneor more cellular layers, and having a repeating geometric pattern of thetype described in the preceding paragraph.

According to yet another embodiment of the present invention, a methodof making a starting material for a multilayer integral geogrid havingone or more cellular layers includes providing a multilayer polymerstarting sheet having one or more layers that are capable of formingsuch layers with a cellular structure as part of the final multilayergeogrid, and providing holes or depressions therein that provide arepeating geometric pattern of partially oriented multilayer junctionsinterconnecting oriented multilayer strands, and defining openings whenthe starting material is biaxially stretched.

According to another embodiment of the present invention, a method ofmaking a multilayer integral geogrid having one or more cellular layersincludes providing a multilayer polymer starting sheet having one ormore layers that are capable of forming such layers with a cellularstructure as part of the final multilayer geogrid, providing holes ordepressions therein, and biaxially stretching the multilayer polymersheet having the holes or depressions therein so as to provide arepeating geometric pattern of partially oriented multilayer junctionsinterconnecting oriented multilayer strands, and defining openingstherein.

And, according to yet another embodiment of the present invention, amethod of strengthening a mass of particulate material includesembedding in the mass of particulate material a multilayer integralgeogrid having one or more cellular layers and having a repeatinggeometric pattern of partially oriented multilayer junctionsinterconnecting oriented multilayer strands defining openings.

Accordingly, it is an object of the present invention to provide amultilayer integral geogrid having one or more cellular layers, so as toprovide an integral geogrid having increased layer compressibility underload. The multilayer integral geogrid having one or more cellular layersmay have a non-cellular layer interposed between two layers with acellular structure, may have a repeating pattern of a non-cellular layerinterposed between two layers with a cellular structure, or may have anon-cellular layer associated with an adjacent layer having a cellularstructure.

Thus, another object of the present invention to provide a startingmaterial for making a multilayer integral geogrid having one or morecellular layers. The multilayer polymer starting sheet includes one ormore layers that are capable of forming the cellular structure. In afirst embodiment, i.e., the foamed embodiment, according to the presentinvention, the layer capable of forming the cellular structure includesa foaming agent which upon extrusion of the layer and/orstretching/orientation of the starting sheet forms the cellular layer aspart of the final multilayer geogrid. In a second embodiment, i.e., thefiller embodiment, according to the present invention, the layer capableof forming the cellular structure includes a particulate fillerdispersed in the layer which upon stretching/orientation of the startingsheet creates the cellular structure in the layer as part of the finalmultilayer geogrid.

Another object of the present invention is to provide multilayerintegral geogrids having one or more cellular layers and having aplurality of oriented multilayer strands interconnected by partiallyoriented multilayer junctions and having an array of openingstherebetween that is produced from a multilayer polymer starting sheet.The multilayer integral geogrid having one or more cellular layers maybe a rectangular geogrid having a repeating geometric pattern ofpartially oriented multilayer junctions interconnecting orientedmultilayer strands defining rectangular openings, a triaxial geogridhaving a repeating geometric pattern of partially oriented multilayerjunctions interconnecting oriented multilayer strands definingtriangular openings, or a geogrid having a repeating geometric patternof partially oriented multilayer junctions interconnecting orientedmultilayer strands defining outer hexagons, each of which surrounds andsupports an inner oriented hexagon, i.e., the “repeating floatinghexagon within a hexagon pattern.”

An associated object of the present invention is to provide a geometrythat can engage with and stabilize a greater variety and range ofquality of aggregates than geometries associated with prior geogridstructures, while at the same time providing an enhancedcompressibility, and other desirable characteristics.

Still another object of the present invention is to provide a soilconstruction that includes a mass of particulate material strengthenedand stabilized by embedding therein a multilayer integral geogrid havingone or more cellular layers and having a repeating geometric pattern asdescribed herein.

Yet another object of the present invention is to provide a method ofmaking a starting material for multilayer integral geogrids having oneor more cellular layers that includes providing a multilayer polymerstarting sheet having one or more layers that are capable of formingsuch layers with a cellular structure as part of the final multilayergeogrid, and providing holes or depressions therein that provide arepeating geometric pattern of partially oriented multilayer junctionsinterconnecting oriented multilayer strands, and defining openings whenthe starting material is biaxially stretched.

The multilayer polymer starting sheet may be produced by coextruding theplurality of layers, or by laminating the plurality of layers to oneanother.

Another object of the present invention is to provide a method of makingmultilayer integral geogrids having one or more cellular layers, whichincludes providing a multilayer polymer starting sheet having one ormore layers that are capable of forming such layers with a cellularstructure as part of the final multilayer geogrid, providing holes ordepressions therein, and biaxially stretching the multilayer polymerstarting sheet so as to provide a repeating geometric pattern ofpartially oriented multilayer junctions interconnecting orientedmultilayer strands, and openings. The method of making theabove-described rectangular opening or triangular opening integralgeogrids can employ known geogrid fabrication methods, such as thosedescribed in the aforementioned U.S. Pat. Nos. 4,374,798, 4,590,029,4,743,486, 5,419,659, 7,001,112, 9,556,580, 10,024,002, and 10,501,896as well as in other patents. The method of making the above-describedintegral geogrid having a repeating geometric pattern of partiallyoriented multilayer junctions interconnecting oriented multilayerstrands, and defining outer hexagons, each of which surrounds andsupports an oriented inner hexagon, can employ a fabrication method asdescribed hereinafter.

More specifically, it is an object of the present invention to provide amethod of making multilayer integral geogrids having one or morecellular layers in which the layer with the cellular structure isproduced by first providing a foamed construction in a layer of themultilayer polymer starting sheet capable of forming such layers, andthen orienting the multilayer polymer starting sheet so as to stretchthe foamed material and create the cellular structure.

Correspondingly, it is another object of the present invention toprovide a method of making multilayer integral geogrids having one ormore cellular layers in which the layer with the cellular structure isproduced by first dispersing a particulate filler in a layer of themultilayer polymer starting sheet capable of forming such layers, andthen orienting the multilayer polymer starting sheet so as to stretchthe dispersion of particulate filler and create the cellular structureas the particulate filler partially separates from the polymeric layermaterial.

And, still another object of the present invention is to provide amethod of strengthening a mass of particulate material that includesembedding in the mass of particulate material a multilayer integralgeogrid having one or more cellular layers, and having a repeatinggeometric pattern of partially oriented multilayer junctionsinterconnecting oriented multilayer strands and openings.

The numerous advantages associated with the multilayer integral geogridhaving one or more cellular layers according to the present inventionare varied in nature.

By virtue of the multilayer integral geogrids having one or morecellular layers of the present invention having not only a multilayerconstruction, but with at least one layer thereof having a cellularstructure, the integral geogrids provide for increased compressibilityof the multilayer integral geogrid under load.

Furthermore, the multilayer nature of the multilayer integral geogridshaving one or more cellular layers of the present invention provides foroverall greater aggregate engagement by the integral geogrid relative tothat of prior monolayer integral geogrids. In addition, by virtue of theone or more cellular layers, the multilayer integral geogrids of thepresent invention are characterized by a structural compliance, i.e.,initial give or flexibility, that leads to better compaction and higherdensity, yet with a final integral geogrid composite stiffness whenincorporated in a soil construction that is greater as a result of theinitial give of the multilayer integral geogrid.

In addition, certain embodiments of the multilayer integral geogridshaving one or more cellular layers of the present invention providehigher aspect ratios on all strands compared to those of prior integralgeogrids. Because the higher aspect ratio associated with certainembodiments of the integral geogrids of the present invention increasesaggregate interlock, the multilayer integral geogrids having one or morecellular layers of the present invention can better accommodate thevarying aspect ratios of aggregate.

In summary, the cellular layers of the multilayer integral geogridaccording to the present invention create unique physical and mechanicalproperties and behaviors in the integral geogrid product. Duringplacement and compaction of aggregate in the multilayer integral geogridit is believed that the nature of the compressible, cellular outerlayers in the ribs and nodes, along with other scientifically engineeredaspects of the geogrid, provides for better initial compatibilitybetween the aggregate and the geogrid, thus improving the aggregatedensity after compaction is complete, and lessening any possibleremaining aggregate movement or repositioning that would normally occurafter compaction and upon initial phases of in service loadings. Whilenot intending to be bound, it is presently believed that theaforementioned initial compatibility of the multilayer integral geogridaccording to the present invention is a key contributor to lessening theamount of deformation that occurs as the geogrid is in use. The benefitof the initial compatibility associated with the present invention isevidenced, for example, by the testing results on a laboratorytrafficking device where significantly fewer passes are required toachieve a stabilized condition of the multilayer integral geogridaccording to the present invention. In addition, various embodiments ofthe multilayer integral geogrid according to the present invention arecharacterized by enhanced rib heights being achieved with less materialthan with prior art geogrids, and increased aspect ratio being achievedwith less material than with prior art geogrids. By virtue of increasedin-plane rib flexibility and pliability and increased out-of-planestiffness, the multilayer integral geogrid of the present inventionprovide for improved geogrid/aggregate interaction, and thus engagement.

Thus, by virtue of the one or more cellular layers, the multilayerintegral geogrids of the present invention provide not only forincreased layer compressibility under load, but for increased aggregateengagement and restraint as an aggregate stabilization product.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described, reference being had tothe accompanying drawings forming a part hereof, wherein like referencenumbers refer to like parts throughout. The accompanying drawings areintended to illustrate the invention, but are not necessarily to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a section of a triaxial three-layerintegral geogrid having two outer layers with a cellular structureaccording to one embodiment of the present invention, with across-sectional view thereof emphasized in the foreground.

FIG. 2 illustrates a uniplanar three-layer polymer starting sheet forthe triaxial multilayer integral geogrid as shown in FIG. 1 , beforeholes or depressions are formed therein.

FIG. 3 is a top perspective plan view of the starting sheet shown inFIG. 2 that has holes punched therein for forming the triaxialthree-layer integral geogrid as shown in FIG. 1 .

FIG. 4 is a perspective cross-sectional view of a section of thestarting sheet shown in FIG. 3 .

FIG. 5 illustrates a uniplanar five-layer polymer starting sheet for atriaxial five-layer integral geogrid having two outer layers and theinnermost layer with a cellular structure, before holes or depressionsare formed therein according to another embodiment of the presentinvention.

FIG. 6 is a perspective cross-sectional view of a section of a triaxialfive-layer integral geogrid having two outer layers and the innermostlayer with a cellular structure associated with the starting sheet shownin FIG. 5 .

FIG. 7 is a plan view of a rectangular three-layer integral geogridhaving two outer layers with a cellular structure according to stillanother embodiment of the present invention.

FIG. 8 is a perspective view of the rectangular three-layer integralgeogrid having two outer layers with a cellular structure shown in FIG.7 .

FIG. 9 is a top perspective plan view of a starting sheet having holesformed therein for forming the rectangular three-layer integral geogridhaving two outer layers with a cellular structure shown in FIG. 7 .

FIG. 10 is a plan view of a hexagonal three-layer integral geogridhaving two outer layers with a cellular structure according to yetanother embodiment of the present invention.

FIG. 11 is a perspective view of the hexagonal three-layer integralgeogrid having two outer layers with a cellular structure shown in FIG.10 .

FIG. 12 is a top perspective view of a starting sheet having holesformed therein for forming the hexagonal three-layer integral geogridhaving two outer layers with a cellular structure shown in FIG. 10 .

FIG. 13 is a perspective view of a hexagonal two-layer integral geogridhaving one cellular layer and one non-cellular layer.

FIG. 14 illustrates a uniplanar two-layer polymer starting sheet for thehexagonal two-layer integral geogrid as shown in FIG. 13 , before holesor depressions are formed therein.

FIG. 15 is a top perspective plan view of the starting sheet havingholes formed therein for forming the hexagonal two-layer integralgeogrid shown in FIG. 13 .

FIG. 16 is a plan view of a possible size and spacing for the holesshown in the starting sheet of FIG. 12 .

FIGS. 17A-17E illustrate a compression mechanism hypothesis of athree-layer integral geogrid having two outer layers with a cellularstructure in accordance with the present invention that is under anapplied load.

FIGS. 18A-18C illustrate a pliable rib mechanism hypothesis of the twoouter layers of a three-layer integral geogrid having two outer layerswith a cellular structure in accordance with the present invention thatis under an applied load, and demonstrates both vertical and horizontalpliability of the integral geogrid.

FIG. 19 presents graphs illustrating a comparison of the non-elastic ribbehavior based on a starting sheet of a conventional monolayer integralgeogrid, versus the elastic rib behavior of a starting sheet of themultilayer integral geogrid having two outer layers with a cellularstructure according to the present invention.

FIG. 20 illustrates the isotropic properties associated with thetriangular geometric features of a triaxial multilayer integral geogridsuch as that depicted in FIGS. 1 and 6 .

FIG. 21 illustrates the isotropic properties associated with thecontinuous ribs in three directions, which is a structural geometricfeature of a hexagonal multilayer integral geogrid such as that depictedin FIGS. 10, 11, and 13 .

FIG. 22 illustrates on a triaxial geogrid an overlay of an open centerhexagon associated with the hexagonal multilayer integral geogrid suchas that depicted in FIGS. 10, 11, and 13 .

FIG. 23 illustrates the open center hexagon and six rib elementsassociated with the hexagonal multilayer integral geogrid such as thatdepicted in FIGS. 10, 11, and 13 .

FIG. 24 is a partial plan view that illustrates the various strandlengths of the hexagonal multilayer integral geogrid such as thatdepicted in FIGS. 10, 11, and 13 .

FIG. 25 illustrates for a hexagonal three-layer integral geogridaccording to the present invention similar to that shown in FIGS. 10 and11 , the effect of increased rib height on surface deformation.

FIG. 26 is a plot of the effect of increased rib height on surfacedeformation associated with the test results presented in FIG. 25 .

FIG. 27 is a table summarizing the effect of increased rib height onsurface deformation associated with the test results presented in FIGS.25 and 26 .

FIG. 28 is a plot of the increased rib height achievable with ahexagonal three-layer integral geogrid according to the presentinvention versus that achievable with a solid monolayer geogrid.

FIG. 29 is a plot of the reduced mass per unit area achievable with ahexagonal three-layer integral geogrid according to the presentinvention versus that achievable with a solid monolayer geogrid

FIG. 30 is a plot of the improved performance achievable with ahexagonal three-layer integral geogrid having compressible, cellularouter layers according to the present invention versus that achievablewith a hexagonal solid monolayer geogrid.

FIG. 31 is a table summarizing the structural data associated with thehexagonal three-layer integral geogrid having compressible, cellularouter layers and the hexagonal solid monolayer geogrid utilized in thetest results presented in FIG. 30 .

FIG. 32 is another plot of the improved performance achievable with ahexagonal three-layer integral geogrid having compressible, cellularouter layers according to the present invention versus that achievablewith a hexagonal solid monolayer geogrid.

FIG. 33 is a table summarizing the structural data associated with thehexagonal three-layer integral geogrid having compressible, cellularouter layers and the hexagonal solid monolayer geogrid utilized in thetest results presented in FIG. 32 .

FIG. 34 is a plot of the improved compressibility achievable with ahexagonal three-layer integral geogrid having compressible, cellularouter layers according to the present invention versus that achievablewith a hexagonal solid monolayer geogrid.

FIG. 35 is a table summarizing the force required to produce a certaincompressibility associated with the hexagonal three-layer integralgeogrid having compressible, cellular outer layers according to thepresent invention and the hexagonal solid monolayer geogrid utilized inthe test results presented in FIG. 34 .

FIG. 36 is a plot of the stiffness achievable with a hexagonalthree-layer integral geogrid having compressible, cellular outer layersaccording to the present invention versus that achievable with ahexagonal solid monolayer geogrid.

FIG. 37 is a table summarizing the stress and strain associated with thehexagonal three-layer integral geogrid having compressible, cellularouter layers and the hexagonal solid monolayer geogrid utilized in thetest results presented in FIG. 36 .

FIG. 38 is a partial plan view that illustrates the various strandlengths of the hexagonal three-layer integral geogrid such as thatdepicted in FIGS. 10 and 11 , and the continuous ribs associated withthe left machine direction, the right machine direction, and thetransverse direction, similar to that shown in FIG. 21 .

FIG. 39 is a plan view of a possible size and spacing for the holesassociated with the starting sheet utilized to produce the hexagonalthree-layer integral geogrid shown in FIG. 38 .

FIG. 40 is aside cross-sectional view of a partial section of ahexagonal three-layer integral geogrid having two outer layers with acellular structure according to the embodiment of the present inventionshown in FIG. 11 .

FIG. 41 illustrates an experimental apparatus used to measure thecompressibility of integral geogrids according to various embodiments ofthe present invention.

FIG. 42 presents a chart illustrating a comparison of thecompressibility, using the apparatus shown in FIG. 41 , of variousembodiments of integral geogrids according to the present inventionversus integral geogrids not having a layer with a cellular structure.

FIG. 43 presents a chart illustrating a comparison of thecompressibility, using the apparatus shown in FIG. 41 , of variousembodiments of integral geogrids according to the present inventionversus other integral geogrids not having a layer with a cellularstructure.

FIG. 44 illustrates another experimental apparatus, a Plate Load TestRig (“PLTR”), used to measure the displacement of integral geogridsaccording to various embodiments of the present invention.

FIG. 45 presents a chart illustrating a comparison of the displacement,using the apparatus shown in FIG. 44 , of various embodiments ofintegral geogrids according to the present invention versus otherintegral geogrids not having a layer with a cellular structure.

FIG. 46 presents another chart illustrating a comparison of thedisplacement, using the apparatus shown in FIG. 44 , of variousembodiments of integral geogrids according to the present inventionversus other integral geogrids not having a layer with a cellularstructure.

FIG. 47 presents a graph illustrating a comparison of the effect ofcompressibility on the relationship between rib aspect ratio and surfacedeformation for two integral geogrids, with one having a layer with acellular structure.

FIG. 48 presents a graph illustrating a comparison of the effect ofcompressibility on the relationship between rib aspect ratio and surfacedeformation for two other integral geogrids, with one having a layerwith a cellular structure.

FIG. 49 presents a graph illustrating a comparison of base geometry onthe ability of rib aspect ratio to influence surface deformation for twointegral geogrids not having a layer with a cellular structure.

FIG. 50 presents a table illustrating a comparison of the benefits ofbase geometry in similarly compressible integral geogrids.

FIG. 51 presents a graph illustrating a comparison of the effect of basegeometry on the relationship between rib aspect ratio and surfacedeformation in similarly compressible integral geogrids.

FIG. 52 presents a table illustrating a comparison, for a single basegeometry, of the effect on surface deformation of the position of thelayer with a cellular structure in multilayer integral geogrids.

FIG. 53 presents a graph illustrating a comparison, for the single basegeometry associated with FIG. 52 , of the effect of the position of thelayer with a cellular structure on the relationship between rib aspectratio and surface deformation.

FIG. 54 presents another table illustrating a comparison, for the singlebase geometry associated with FIG. 52 , of the effect on surfacedeformation of the position of the layer with a cellular structure inmultilayer integral geogrids.

FIG. 55 presents another graph illustrating a comparison, for the singlebase geometry associated with FIG. 52 , of the effect of the position ofthe layer with a cellular structure on the relationship between ribaspect ratio and surface deformation.

FIG. 56 presents a table illustrating a comparison, for the integralgeogrid according to the present invention having the single basegeometry associated with FIG. 52 and a prior art geogrid not having alayer with a cellular structure, of the effect on surface deformation ofthe layer with a cellular structure.

FIG. 57 presents a graph illustrating a comparison, for the integralgeogrid according to the present invention having the single basegeometry associated with FIG. 52 and a prior art geogrid not having alayer with a cellular structure, of the effect of the compressibility ofthe layer with a cellular structure on the relationship between ribaspect ratio and surface deformation.

FIG. 58 presents a graph illustrating compression force versusdisplacement data for a soft foam embodiment of the present invention.

FIG. 59 presents a graph illustrating compression force versusdisplacement data for a hard foam embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although only preferred embodiments of the present invention areexplained in detail, it is to be understood that the invention is notlimited in its scope to the details of construction and arrangement ofcomponents set forth in the following description or illustrated in thedrawings. As described hereinafter, the present invention is capable ofother embodiments and of being practiced or carried out in various ways.

Also, in describing the preferred embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart, and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose.

As used herein, the term “cellular” is used according to a commonlyaccepted definition, i.e., pertaining to a material having dispersedtherein a plurality of voids, cavities, pores, fissures, bubbles, holes,or other types of openings produced according the methods describedherein. Similarly, the term “non-cellular” means a material notcontaining the voids, cavities, pores, bubbles, holes, or other types ofopenings produced according the methods described herein, i.e., so as tohave a structure that is generally continuous or solid in nature. Theaforementioned voids, cavities, pores, fissures, bubbles, holes, orother types of openings produced according the methods described hereinthat provide the cellular structure are sometimes herein referred to as“cellular openings.”

And, as used herein, the terms “coextruded,” “coextruding,” and“coextrusion” are used according to their commonly accepted definition,i.e., pertaining to a process starting with two or more polymericmaterials that are extruded together and shaped in a single die to forma multilayer sheet.

As also used herein, the terms “laminated,” “laminating,” and“lamination” are used according to their commonly accepted definition,i.e., pertaining to a process starting with two or more polymericmaterial sheets that are produced individually in one manufacturingprocess, and then are joined or bonded to each other in anothermanufacturing step to thereby create a multilayer sheet of two or morelayers.

And, as used herein, the term “crush fit” is used to describe a materialthat is sufficiently compressible such that it will conform, physicallyadapt, and reshape to match the shape and texture of any stronger and/orstiffer material above or on top of it once sufficient force is applied.

According to one preferred embodiment of the present invention, themultilayer integral geogrid having one or more cellular layers has anon-cellular layer interposed between two outer layers with a cellularstructure to form a three-layer integral geogrid. According to anotherembodiment of the present invention, the multilayer integral geogridhaving one or more cellular layers has a repeating pattern of anon-cellular layer interposed between two layers with cellularstructures. According to still another embodiment of the presentinvention, the multilayer integral geogrid having one or more cellularlayers has a non-cellular layer associated with an adjacent single layerhaving a cellular structure.

More specifically, the multilayer integral geogrids having one or morecellular layers include a plurality of oriented multilayer strandsinterconnected by partially oriented multilayer junctions and having anarray of openings therebetween, with each of the oriented multilayerstrands and each of the partially oriented multilayer junctions having aplurality of layers including one or more cellular layers, and with theplurality of layers being in contact both along each of the orientedmultilayer strands and each of the partially oriented multilayerjunctions.

Even more specifically, the one or more cellular layers contain adistribution of a plurality of voids, cavities, pores, bubbles, holes,or other types of openings therein. This cellular structure may beassociated with a foamed construction of the layer, or may be associatedwith a particulate filler that is distributed throughout the layer inorder to create expansion of the cellular layer in the final multilayerintegral geogrid.

And, as also used herein, the term “expansion” when used to describe theaforementioned one or more cellular layers refers to the ability of thecellular layer to expand during the various stages of forming themultilayer integral geogrid according to the present invention. The term“expanded” when used to describe the aforementioned one or more cellularlayers means the structure of the cellular layer after the formation ofthe multilayer integral geogrid via stretching to orient the geogrid,including the associated deformation (including an expansion in size) ofthe plurality of voids, cavities, pores, fissures, bubbles, holes, orother types of openings present in the cellular layer, i.e., thecellular openings.

Furthermore, the multilayer construction may include layers that arecoextruded, or layers that are laminated. The expansion of the layerwith the cellular structure may occur during extrusion/lamination orstretching/orientation, or both. And, the resulting multilayer integralgeogrid having one or more cellular layers and having the plurality oforiented multilayer strands interconnected by the partially orientedmultilayer junctions and having an array of openings therebetween may beconfigured in any of a variety of repeating geometric patterns, such asdescribed herein.

As shown in FIG. 1 , a three-layer integral geogrid 200 according to oneembodiment of the present invention (here a triaxial integral geogrid)includes, disposed between a first cellular outer layer 210 and a secondcellular outer layer 230, a third layer, i.e., a non-cellular innerlayer 220.

As indicated above, the first cellular outer layer 210 and the secondcellular outer layer 230 contain a distribution of cellular openings 250therein. The cellular openings 250 may be associated with a foamedconstruction of the first cellular outer layer 210 and the secondcellular outer layer 230, with the cellular openings having been formedinitially during coextrusion of the starting sheet and subsequentlydeformed in shape, i.e., expanded in size, by the stretching of theperforated starting sheet during the formation of the integral geogrid.Or, the cellular openings 250 may be associated with a particulatefiller that is distributed in the first cellular outer layer 210 and thesecond cellular outer layer 230, with the cellular openings having beencreated adjacent to the particulate filler by the stretching of theperforated starting sheet during the formation of the integral geogrid.

According to the foamed embodiment of the first cellular outer layer 210and the second cellular outer layer 230, the instant invention caninclude the use of a foaming agent to provide an expanded first cellularouter layer 210 and an expanded second cellular outer layer 230, i.e.,each having a cellular foamed structure. That is, according to anembodiment of the invention that produces the layers of the integralgeogrid via coextrusion (discussed below), one possible process is tomix a chemical foaming agent with the polymer that is extruded to formthe expanded first cellular outer layer 210 and the expanded secondcellular outer layer 230. The heat that is generated to melt the polymerdecomposes the chemical foaming agent, which results in the liberationof a gas. The gas is then dispersed in the polymer melt, and expandsupon exiting the die. As a result, the first outer layer 210 and thesecond outer layer 230 are foamed to create the cellular layers, i.e.,layers that have a plurality of cellular openings. Similar to chemicalfoaming, the injection of a gas that results in formation of the firstcellular outer layer 210 and the second cellular outer layer 230 is alsoconsidered a foaming process according to this embodiment of theinvention.

According to the particulate filler embodiment of the first cellularouter layer 210 and the second cellular outer layer 230, the instantinvention employs a dispersion of a particulate filler to provideexpanded first cellular outer layer 210 and second cellular outer layer230, i.e., each having a cellular structure. The inclusion of such aparticulate filler in the first cellular outer layer 210 and the secondcellular outer layer 230 creates a product having a thicker, i.e.,loftier, profile, which can lead to enhanced performance of the integralgeogrid in certain service applications. Depending upon the serviceapplication in which the multilayer integral geogrid is to be employed,such particulate fillers, may include, for example, one or more of CaCO₃(calcium carbonate), hydrous magnesium silicates (talc), CaSiO₃(wollastonite), calcium sulphate (gypsum), diatomaceous earth, titaniumdioxide, nano-fillers (such as nano clay), multi-wall carbon nanotube(“MWCNT”), single wall carbon nanotube (“SWCNT”), natural or syntheticfibers, metal fibers, glass fibers, dolomite, silica, mica, and aluminumhydrate.

According to both the foamed embodiment and the filler embodiment, thematerial of construction of the first cellular outer layer 210 and thematerial of construction of the second cellular outer layer 230 may bethe same as each other, or may be different from one another, althoughthe same material is preferred. In general, the material of constructionof the non-cellular inner layer 220 is different from the material ofconstruction of the first cellular outer layer 210 and the material ofconstruction of the second cellular outer layer 230.

Contemplated embodiments of the invention include one in which one ormore of the foamed layers are used in conjunction with one or more solidlayers, one in which one or more of the filler layers are used inconjunction with one or more solid layers, and one in which one or moreof the foamed layers and one or more of the filler layers are used inconjunction with one or more solid layers.

FIG. 2 illustrates a uniplanar three-layer polymer starting sheet 100for the three-layer integral geogrid having one or more cellular layers200 shown in FIG. 1 , before holes or depressions are formed therein.

As shown in FIG. 2 , the multilayer polymer starting sheet 100 is athree-layer sheet embodiment of the invention. That is, preferably,sheet 100 includes a first expansion outer layer 110, a second expansionouter layer 130, and a non-cellular inner layer 120. The first expansionouter layer 110 and the second expansion outer layer 130 are arranged onopposite planar surfaces of the non-cellular inner layer 120, preferablyin a uniplanar or substantially uniplanar configuration. Furthermore,while the three-layer configuration of sheet 100 is shown for purposesof illustration, the invention contemplates the use of a sheet havingmultiple layers arranged in various configurations, multiple layershaving various combinations of thicknesses, and multiple layers havingvarious materials of construction, all as dictated by the particularapplication in which the integral geogrid is to be employed. Forexample, while the three-layer configuration of sheet 100 is shown forpurposes of illustration, the invention also contemplates the use ofsheets having more than three layers. In general, the layerconfiguration, the layer thicknesses, and the materials of constructionof the layers are selected to provide not only ease of fabrication ofthe integral geogrid, but also an integral geogrid having the desireddegree of compressibility, stiffness, and other performance properties.

Furthermore, according to another embodiment of the present invention,the multilayer integral geogrid may have two layers, i.e., anon-cellular layer associated with a single adjacent layer having acellular structure. Geogrids are typically installed on top of a soilformation such as clay, silt or sand. All of the aforementionedmaterials are “fine grained” materials, i.e., materials characterized byparticle sizes that are a very small fraction of the size of the geogridapertures. And then, typically, “large” (i.e., 0.25 inch to 3 inchdiameter) particle granular aggregates are installed on top of thegeogrid. It is hypothesized that the compressible, i.e., cellular, layeris best situated such that the granular aggregates are placed on top ofthe compressible layer. It is believed to be less important to havecompressible layers in contact with the fine grained soils. Accordingly,such a two-layer integral geogrid would have a solid layer on the bottomand a compressible layer on top when installed.

As shown in FIG. 13 (described in detail below), the multilayer integralgeogrid 1500 according to the present invention has the above-describednon-cellular layer associated with a single adjacent layer having acellular structure. That is, instead of having a non-cellular layerdisposed between two cellular layers, a two-layer integral geogrid 1500in accordance with the present invention has one cellular layer 1510 andone non-cellular layer 1520. As shown in FIG. 14 , the two-layer polymerstarting sheet 1700 associated with the two-layer integral geogridembodiment of the invention includes an expansion outer layer 1710 and anon-cellular layer 1720.

As described above, the three-layer polymer starting sheet 100 used asthe starting material for a three-layer integral geogrid according tothe present invention is preferably through-punched, although it may bepossible to use depressions formed therein instead. According to theembodiment in which depressions are formed in the sheet, the depressionsare provided on each side of the sheet 100, i.e., on both the top andthe bottom of the sheet. Furthermore, the depressions extend into eachlayer of the multilayer sheet.

According to a preferred embodiment of the present invention, theoverall thickness of the three-layer polymer starting sheet 100 is fromabout 2 mm to about 12 mm and, according to a more preferred embodimentof the invention, the overall thickness of the sheet 100 is from about 4mm to about 10 mm.

With regard to the individual thicknesses of the sheet layers, accordingto a preferred embodiment of the invention, the thickness of the firstexpansion outer layer 110 is from about 0.5 mm to about 4 mm, thethickness of the non-expanded inner layer 120 is from about 0.5 mm toabout 4 mm, and the thickness of the second expansion outer layer 130 isfrom about 0.5 mm to about 4 mm, keeping in mind that the overallthickness of the starting sheet 100 is from about 2 mm to about 12 mm.And, according to a more preferred embodiment of the invention, thethickness of the first expansion outer layer 110 is from about 1 mm toabout 3 mm, the thickness of the non-expanded inner layer 120 is fromabout 1 mm to about 3 mm, and the thickness of the second expansionouter layer 130 is from about 1 mm to about 3 mm.

In general, the layers of the starting sheet are polymeric in nature.The polymer material of the first expansion outer layer 110, thenon-cellular inner layer 120, and the second expansion outer layer 130may be the same as each other, or may be different from one another.Preferably, the material of construction of the first expansion outerlayer 110 and the material of construction of the second expansion outerlayer 130 are the same as each other. More preferably, the material ofconstruction of the non-cellular inner layer 120 is different from thematerial of construction of both the first expansion outer layer 110 andthe material of construction of the second expansion outer layer 130.

For example, the materials of construction may include high molecularweight polyolefins, and broad molecular weight distribution polymers. Asis known to one skilled in the art of polymer science, the term “highmolecular weight” polyolefin means a resin with a Melt Flow Rate (“MFR”;also known as Melt Flow Index (“MFI”)) as determined by ASTM D 1238-20of less than 1. As is also known, the term “broad molecular weightdistribution” polymer means a resin having molecular chains that vary insize and are depicted by a wide binomial distribution curve on amolecular weight distribution graph. Furthermore, the polymericmaterials may be virgin stock, or may be recycled materials, such as,for example, post-industrial or post-consumer recycled polymericmaterials. And, the use of one or more polymeric layers having a lowercost than that of the aforementioned high molecular weight polyolefinsand broad specification polymers is also contemplated. According to apreferred embodiment of the invention, the material of construction ofthe first expansion outer layer 110 and the material of construction ofthe second expansion outer layer 130 is a broad specification polymer,such as, for example, a virgin polypropylene (“PP”), or a recycled PP,such as, for example, a post-industrial PP or other recycled PP. As usedherein, the term broad specification polymer means a polymer having anMFR (or MFI) as measured by ASTM D 1238-20, of from 1 to 6, and an ashcontent as measured by ASTM D 4218-20 of less than 6%. And, according tothe same preferred embodiment, the material of construction of thenon-cellular inner layer 120 is a high molecular weight polyolefin, suchas, for example, a PP. However, depending upon the particularapplication of the integral geogrid, polymeric components having amaterial of construction other than polypropylene may be included in themultilayer polymer starting sheet 100.

According to the present invention, the multilayer polymer startingsheet 100 may be produced by coextrusion of the layers, such as isdisclosed in the aforementioned '960 application, or by lamination ofseparately produced layers. For example, lamination of separatelyproduced layers can be accomplished by reheating and softening onesurface of each of the separately produced layers, layering one upon theother such that the reheated and softened surfaces are adjacent oneanother, and then applying pressure resulting in the fusion of theseparately produced sheets to one another.

FIG. 3 is a top perspective plan view of the multilayer polymer startingsheet 100 shown in FIG. 2 that has holes 140 punched therein for formingthe triaxial three-layer integral geogrid 200 shown in FIG. 1 . FIG. 4is a perspective cross-sectional view of a section of the three-layerpolymer starting sheet 100 shown in FIG. 3 .

The size and spacing of the holes 140 shown in FIG. 4 are as disclosedin the Walsh '112 patent. Per FIG. 1 , the triaxial three-layer integralgeogrid 200 having one or more cellular layers includes highly orientedstrands 205 and partially oriented junctions 235, also as disclosed inthe Walsh '112 patent. The second expansion outer layer 130 of thethree-layer polymer starting sheet 100 (shown in FIG. 3 ) has beenstretched and oriented into the second cellular outer layer 230 of thestrands 205 and junctions 235. Similarly, the first expansion outerlayer 110 of the three-layer polymer starting sheet 100 has beenstretched and oriented into the second cellular outer layer 210 of thestrands 205 and junctions 235. As the second expansion outer layer 130and first expansion outer layer 110 are being stretched and oriented,the non-cellular inner layer 120 is also being stretched and orientedinto middle layer 220 of both the strands 205 and junctions 235.

As indicated above, while the three-layer configuration of multilayerpolymer starting sheet 100 has been shown for purposes of illustration,the present invention also contemplates multilayer integral geogridswith one or more cellular layers which have more than three layers, andthe use of starting sheets having more than three layers.

For example, the starting sheet can be a five-layer configuration, suchas multilayer polymer starting sheet 400 shown in FIG. 5 . Startingsheet 400 includes a middle expansion layer 420, a first non-cellularinner layer 410, a second non-cellular inner layer 430, a firstexpansion outer layer 440, and a second expansion outer layer 450. Thefirst non-cellular inner layer 410 and the second non-cellular innerlayer 430 are arranged on opposite planar surfaces of middle expansionlayer 420, preferably in a uniplanar or substantially uniplanarconfiguration. The first expansion outer layer 440 and the secondexpansion outer layer 450 are arranged on opposite planar surfaces of,respectively, first non-cellular inner layer 410 and second non-cellularinner layer 430, preferably in a uniplanar or substantially uniplanarconfiguration.

In the particular embodiment of the invention shown in FIG. 5 , themultilayer polymer starting sheet 400 is made by coextruding orlaminating a first material that forms the middle expansion layer 420, asecond material that forms the first non-cellular inner layer 410, athird material that forms the second non-cellular inner layer 430, afourth material that forms the first expansion layer 440, and a fifthmaterial that forms the second expansion outer layer 450.

In general, the polymeric material of the middle expansion layer 420,the first non-cellular inner layer 410, the second non-cellular innerlayer 430, the first expansion outer layer 440, and the second expansionouter layer 450 may be the same as each other, or may be different fromone another. For example, the middle expansion layer 420 may have afirst material of construction, the first non-cellular inner layer 410and the second non-cellular inner layer 430 may have a second materialof construction, and the first expansion outer layer 440 and the secondexpansion outer layer 450 may have a third material of construction. Insummary, depending upon the particular service application in which thefive-layer integral geogrid having a layer or layers with a cellularstructure made from the sheet 400 is to be employed, variouscombinations of materials of construction for the above-described fivelayers may be used.

FIG. 6 is a perspective view of a section of a triaxial five-layerintegral geogrid 500 having three or more cellular layers associatedwith the five-layer polymer starting sheet 400 shown in FIG. 5 . Thetriaxial five-layer integral geogrid 500 having three or more cellularlayers includes highly oriented multilayer strands 505 and partiallyoriented multilayer junctions 535. After holes have been punched insheet 400, the first expansion outer layer 440 and the second expansionouter layer 450 of sheet 400 have been stretched and oriented into,respectively, the first cellular outer layer 540 and the second cellularouter layer 550 of the multilayer strands 505 and multilayer junctions535. Similarly, the first non-cellular inner layer 410 and the secondnon-cellular inner layer 430 of sheet 400 have been stretched andoriented into, respectively, the first non-cellular inner layer 510 andthe second non-cellular inner layer 530 of the strands 505 and junctions535. And, as the first expansion outer layer 440 and the secondexpansion outer layer 450, and the first non-cellular inner layer 410and the second non-cellular inner layer 430 are being stretched andoriented, the middle expansion layer 420 is also being simultaneouslystretched and oriented into middle cellular layer 520 of both themultilayer strands 505 and multilayer junctions 535. And again, as withmultilayer polymer starting sheet 100 (i.e., the three-layerembodiment), multilayer polymer starting sheet 400 having five layersmay have expansion layers that are foamed or that have filler, and maybe formed by coextrusion or lamination.

According to a preferred embodiment of the present invention, theoverall thickness of the five-layer integral geogrid 500 is from about 1mm to about 6 mm and, according to a more preferred embodiment of theinvention, the overall thickness of the five-layer integral geogrid 500is from about 1.5 mm to about 3.5 mm.

With regard to the individual thicknesses of the layers of thefive-layer integral geogrid 500, according to a preferred embodiment ofthe invention, the thickness of the first cellular outer layer 540 isfrom about 0.1 mm to about 2 mm, the thickness of the second cellularouter layer 550 is from about 0.1 mm to about 2 mm, the thickness of thefirst non-cellular inner layer 510 is from about 0.1 mm to about 2 mm,the thickness of the second non-cellular inner layer 530 is from about0.1 mm to about 2 mm, and the thickness of the middle non-cellular layer520 is from about 0.1 mm to about 2 mm.

Now, turning to the geometry of the multilayer integral geogrids havingone or more cellular layers, the invention contemplates at least threegeneral categories: triangular (such as “triaxial”), rectangular, andhexagonal.

The geometry of the triaxial expanded multilayer integral geogrid 200 isas shown in FIGS. 1 (three-layer) and 6 (five-layer).

The geometry of a rectangular multilayer integral geogrid 700 having oneor more cellular layers is shown in FIG. 7 . The rectangular multilayerintegral geogrid 700 having one or more cellular layers includes highlyoriented multilayer strands 705 and partially oriented multilayerjunctions 710. As shown in FIG. 8 , a rectangular three-layer integralgeogrid 700 having two or more cellular layers includes, disposedbetween a first cellular outer layer 710 and a second cellular outerlayer 730, a third layer, i.e., a non-cellular inner layer 720. As withthe triangular geometry described herein, the first cellular outer layer710 and the second cellular outer layer 730 contain a distribution ofcellular openings 750 therein. The cellular openings 750 may beassociated with a foamed construction of the first cellular outer layer710 and the second cellular outer layer 730, or may be associated with aparticulate filler that is distributed in the first cellular outer layer710 and the second cellular outer layer 730.

The second expansion outer layer 630 of a three-layer polymer startingsheet 600 (described below) has been stretched and oriented into thesecond cellular outer layer 730 of the multilayer strands 705 andmultilayer junctions 740. Similarly, the first expansion outer layer 610of the multilayer polymer starting sheet 600 has been stretched andoriented into the first cellular outer layer 710 of the multilayerstrands 705 and multilayer junctions 740. As the second cellular outerlayer 730 and first cellular outer layer 710 are being stretched andoriented, the non-cellular inner layer 620 is also being simultaneouslystretched and oriented into non-cellular inner layer 720 of both themultilayer strands 705 and multilayer junctions 740.

FIG. 9 is a top perspective plan view of a three-layer polymer startingsheet section 600 that has holes 640 punched therein for forming therectangular three-layer integral geogrid 700 shown in FIGS. 7 and 8 .The multilayer polymer starting sheet 600 includes, disposed between afirst expansion outer layer 610 and a second expansion outer layer 630,a third layer, i.e., a non-cellular inner layer 620. As with thetriangular geometry described herein, the first expansion outer layer610 and the second expansion outer layer 630 form a distribution ofcellular openings 650 in the final integral geogrid 700 shown in FIGS. 7and 8 .

And, as with the triangular geometry embodiment of the multilayerintegral geogrid having one or more cellular layers, the rectangularembodiment of the multilayer integral geogrid one or more cellularlayers has a cellular layer that is either foamed or contains aparticulate filler. And, the starting sheet of the rectangularembodiment of the multilayer integral geogrid having one or morecellular layers is the same as previously disclosed herein for thetriangular embodiment, and may be formed by coextrusion or lamination.

And finally, the geometry of a hexagonal multilayer (here, three-layer)integral geogrid 1100 having one or more cellular layers is as shown inFIGS. 10 and 11 . The impetus for the development of the hexagonalmultilayer integral geogrid having one or more cellular layers is thatit is structurally and economically advantageous to produce an integralgeogrid having a structure and geometry with the ability to engage withand stabilize a wide variety and range of quality of aggregates that issuitable for the demands of service applications such as geosyntheticreinforcement or having other properties desirable for particulargeosynthetic applications.

The hexagonal multilayer integral geogrid having one or more cellularlayers is designed to improve upon a triaxial integral geogrid byretaining the isotropic properties of the triaxial geometry whilesubstantially enhancing aggregate support and interaction. The keyimprovements of the hexagonal multilayer integral geogrid over thetriaxial geometry and other prior art geometries relate to at least twokey design features. First, with respect to geometry, the hexagonalmultilayer integral geogrid retains the 360-degree properties of thetriaxial geometry by retaining every other rib in each of three ribdirections as continuous ribs. However, the hexagonal multilayerintegral geogrid converts every other node along the non-continuous ribsfrom a non-functional element (a node) into a functional feature—a newopen hexagon that comprises six new rib elements. These six new ribelements are now functional features rather than one non-functionalnode. The open hexagon and the six rib elements substantially increasethe degree to which the hexagonal multilayer integral geogrid caninteract with and support aggregate. In addition, the hexagonalmultilayer integral geogrid geometry provides continuous ribs in threedirections, which provides 360-degree strength and stability properties.This is done in a variety of ways including, as described above,converting non-functional nodes to functional elements, and improvingmacro-interaction by incorporating higher ribs.

Second, according to one embodiment of the invention, the coextrudedhexagonal multilayer integral geogrid utilizes the multilayerconstruction and the foam or filler enhancements described herein. Thatis, by virtue of the coextruded multilayer construction and the cellularstructures of the outer two layers, the invention provides formicro-interaction associated with top and bottom layers of compressiblepolymer designed to nest aggregate particles and facilitate and maintainmaximum properties of the aggregate. This advanced coextrusion processtechnology also yields other benefits in production and manufacturing,such as improved adhesion between layers due to simultaneous extrusion,controlled creation of cellular structure while maintaining appropriaterelative velocity and shear rate between the layers, and cost reductiondue to the single step process of making the multilayer sheet. In short,the combining together of these design features into the hexagonalmultilayer integral geogrid results in significantly better performancethan a triaxial geogrid, and yields various production and manufacturingbenefits that allow this new and novel geogrid to be produced with onlyminor incremental cost increase.

To attain the aforementioned ability to engage with and stabilize agreater variety and range of quality of aggregates than geometriesassociated with prior geogrid structures, while simultaneously providinga variety of degrees of localized out-of-plane and in-plane stiffness,the hexagonal multilayer integral geogrid having one or more cellularlayers of the present invention has a repeating pattern ofinterconnected oriented multilayer strands and partially orientedmultilayer junctions which form a repeating pattern of outer hexagons,each of which supports and surrounds an oriented multilayer innerhexagon to define three different shaped openings of a multi-axialintegral geogrid. To provide additional strength and stability, thegeometry of the outer hexagons forms linear strands that extendcontinuously throughout the entirety of the multi-axial integral geogridin three different directions.

As so formed, the inner multilayer hexagon is comprised of six orientedmultilayer strands and is supported by six oriented multilayerconnecting strands which extend from the partially oriented multilayerjunctions of the outer hexagon to a respective corner of the innerhexagon to form oriented multilayer tri-nodes. The multilayer tri-nodeshave a much higher level of orientation than the multilayer junctions,and tend towards being fully oriented. This configuration creates aninner multilayer hexagon that is suspended, i.e., floating, relative tothe outer multilayer hexagon structure. This structure allows the innermultilayer hexagon to shift up or down so as to “float” or flex (i.e.,deform) relative to the primary plane of the integral geogrid, duringplacement and compaction of the aggregate, which enhances the integralgeogrid's ability to engage and stabilize the aggregate. As noted above,the foregoing integral geogrid structure is herein referred to as amultilayer integral geogrid having a “repeating floating hexagon withina hexagon pattern or simply a “hexagonal” multilayer integral geogrid.

Referring now to FIGS. 10 and 11 , the hexagonal three-layer integralgeogrid 1100 having one or more cellular layers includes a plurality ofinterconnected, oriented multilayer strands having an array of openingstherein, a repeating floating hexagon within a hexagon pattern of theinterconnected, oriented multilayer strands and the openings, andincluding linear multilayer strands that extend continuously throughoutan entirety of the multi-axial integral geogrid. These linear multilayerstrands that extend continuously throughout an entirety of themulti-axial integral constitute strong axis strands. More specifically,the hexagonal three-layer integral geogrid 1100 having one or morecellular layers includes a repeating pattern of floating inner hexagons1130 within each outer hexagon 1110. The outer hexagon 1110 includes aplurality of outer oriented multilayer strands or ribs 1120interconnected by partially oriented multilayer junctions 1115. Theinner hexagon 1130 includes a plurality of oriented multilayerconnecting strands 1145 and 1150 interconnected by multilayer tri-nodes1135, and defines a hexagon-shaped center opening 1170. The outerhexagon 1110 is connected to the smaller inner hexagon 1130 by aplurality of multilayer supporting strands 1140 and 1160, which define aplurality of trapezoid-shaped openings 1180. At the center of eachpattern of three adjacent outer hexagons 1110 is a triangular shapedopening 1190. As shown, junctions 1115 are much larger than tri-nodes1135.

In another aspect of the hexagonal geometry embodiment of the instantinvention, the supporting strands 1140 and 1160, which extend inwardlyfrom the partially oriented junctions 1115 and connect with thetri-nodes 1135 of the floating inner hexagon 1130 (or such other innergeometric configurations described herein), which is supported by suchsupporting strands, constitute “engineered discontinuities” or “floatingengineered discontinuities.”

As is evident from FIG. 10 , another feature of the hexagonalthree-layer integral geogrid 1100 having one or more cellular layers ofthe present invention is the linearly continuous nature of the outermultilayer strands 1120 of the repeating outer hexagon pattern. That is,the oriented multilayer strands 1120 are linearly continuous, viapartially oriented multilayer junctions 1115, as they extendcontinuously throughout the entirety of the multi-axial integral geogridin three different directions separated from each other by approximately120°, and indicated by arrows 120A, 120B, and 120C in FIGS. 10 and 11 .These linear multilayer strands that extend continuously throughout anentirety of the multi-axial integral constitute strong axis strands.Those skilled in the art will appreciate that different orientations ofthe same basic geometry are possible after stretching, if an appropriatecorresponding rotation of the punched starting sheet geometry is made.The linearly continuous nature of the multilayer strands 1120 providesboth enhanced strength and in-plane stiffness to the hexagonalmultilayer integral geogrid having one or more cellular layers of thepresent invention.

Preferably, the thickness of the hexagonal three-layer integral geogrid1100 having two outer cellular layers at its thickest dimension (atjunctions 1115) is from about 1.5 mm to about 10 mm and, morepreferably, such thickness of the multi-axial expanded three-layerintegral geogrid 1100 is from about 4 mm to about 8 mm.

With regard to the geometry of the integral geogrid, FIG. 20 illustratesthe isotropic properties associated with the triangular geometricfeatures of a triaxial multilayer integral geogrid such as that depictedin FIGS. 1 and 6 . And, FIG. 21 illustrates the isotropic propertiesassociated with the continuous ribs in three directions, which is astructural geometric feature of a hexagonal multilayer integral geogridsuch as that depicted in FIGS. 10, 11, and 13 .

Additionally, FIG. 22 illustrates on a triaxial geogrid an overlay of anopen center hexagon associated with the hexagonal multilayer integralgeogrid such as that depicted in FIGS. 10, 11, and 13 . And, FIG. 23illustrates the open center hexagon and six rib elements associated withthe hexagonal multilayer integral geogrid such as that depicted in FIGS.10, 11, and 13 .

FIG. 24 is a partial plan view that illustrates the various strandlengths of the hexagonal multilayer integral geogrid such as thatdepicted in FIGS. 10, 11, and 13 .

Additionally, FIG. 38 is a partial plan view that illustrates thevarious strand lengths of the hexagonal three-layer integral geogridsuch as that depicted in FIGS. 10 and 11 , and the continuous ribsassociated with the left machine direction, the right machine direction,and the transverse direction, similar to that shown in FIG. 21 . FIG. 39is a plan view of a possible size and spacing for the holes associatedwith the starting sheet utilized to produce the hexagonal three-layerintegral geogrid shown in FIG. 38 . And, FIG. 40 is asidecross-sectional view of a partial section of a hexagonal three-layerintegral geogrid having two outer layers with a cellular structureaccording to the embodiment of the present invention shown in FIG. 11 .

Now, more specifically, turning back to FIG. 24 , for one embodiment ofa hexagonal three-layer integral geogrid according to the presentinvention as shown in FIG. 24 , the multilayer integral geogrid has aRib A height having a broad range of from 1 mm to 4 mm, a preferredrange of from 2 mm to 3 mm, and a preferred dimension of 1.97 mm. TheRib A width has a broad range of from 0.75 mm to 3 mm, a preferred rangeof from 1 mm to 2 mm, and a preferred dimension of 1.6 mm. The Rib Alength has a broad range of from 30 mm to 45 mm, a preferred range offrom 35 mm to 40 mm, and a preferred dimension of 37 mm. The Rib Aaspect ratio has a broad range of from 1:1 to 3:1, a preferred range offrom 1.5:1 to 1.8:1, and a preferred value of 1.7:1.

The Rib B height has a broad range of from 1 mm to 3 mm, a preferredrange of from 1.5 mm to 2.5 mm, and a preferred dimension of 1.6 mm. TheRib B width has a broad range of from 0.75 mm to 3.5 mm, a preferredrange of from 1 mm to 3 mm, and a preferred dimension of 1.8 mm. The RibB length has a broad range of from 15 mm to 25 mm, a preferred range offrom 18 mm to 22 mm, and a preferred dimension of 21 mm. The Rib Baspect ratio has a broad range of from 0.75:1 to 2:1, a preferred rangeof from 1.2:1 to 1.4:1, and a preferred value of 1.3:1.

The Rib C height has a broad range of from 1 mm to 4 mm, a preferredrange of from 2 mm to 3 mm, and a preferred dimension of 2.7 mm. The RibC width has a broad range of from 0.75 mm to 3.5 mm, a preferred rangeof from 1 mm to 2.5 mm, and a preferred dimension of 1.6 mm. The Rib Clength has a broad range of from 15 mm to 30 mm, a preferred range offrom 20 mm to 25 mm, and a preferred dimension of 23 mm. The Rib Caspect ratio has a broad range of from 1:1 to 3:1, a preferred range offrom 1.5:1 to 2.5:1, and a preferred value of 1.7:1.

The Rib D height has a broad range of from 1.5 mm to 4 mm, a preferredrange of from 2 mm to 3.5 mm, and a preferred dimension of 2.3 mm. TheRib D width has a broad range of from 1 mm to 4 mm, a preferred range offrom 1.5 mm to 2.5 mm, and a preferred dimension of 1.5 mm. The Rib Dlength has a broad range of from 10 mm to 30 mm, a preferred range offrom 15 mm to 25 mm, and a preferred dimension of 18 mm. The Rib Daspect ratio has a broad range of from 1:1 to 3:1, a preferred range offrom 1.4:1 to 1.7:1, and a preferred value of 1.6:1.

The Rib E height has a broad range of from 1 mm to 4 mm, a preferredrange of from 1.5 mm to 3.0 mm, and a preferred dimension of 1.9 mm. TheRib E width has a broad range of from 0.75 mm to 3.5 mm, a preferredrange of from 1 mm to 3 mm, and a preferred dimension of 1.7 mm. The RibE length has a broad range of from 15 mm to 30 mm, a preferred range offrom 20 mm to 25 mm, and a preferred dimension of 22 mm. The Rib Easpect ratio has a broad range of from 0.75:1 to 2:1, a preferred rangeof from 1:1 to 1.5:1, and a preferred value of 1.3:1. The Major Nodethickness has a broad range of from 1.5 mm to 10 mm, a preferred rangeof from 3 mm to 8 mm, and a preferred dimension of 5.1 mm.

And, as shown in FIG. 40 , for one embodiment of the hexagonalthree-layer integral geogrid according to the present invention, whichhas a first and a second compressible, cellular outer layer arranged onopposite surfaces of an inner non-cellular layer, the multilayerintegral geogrid has a lower junction (i.e., junction 1115; see FIG. 11) cap thickness (dimension “A”) having a broad range of from 1 mm to 3mm, a preferred range of from 1.5 mm to 2.5 mm, and a preferreddimension of 1.7 mm; an upper junction cap thickness (dimension “B”)having a broad range of from 1 mm to 3 mm, a preferred range of from 1.5mm to 2.5 mm, and a preferred dimension of 1.7 mm; a central junctioncore thickness (dimension “C”) having a broad range of from 1 mm to 3mm, a preferred range of from 1.5 mm to 2.5 mm, and a preferreddimension of 1.7 mm; a rib A (see FIG. 24 ) lower cap thickness(dimension “D”) having a broad range of from 0.4 mm to 1 mm, a preferredrange of from 0.5 mm to 0.8 mm, and a preferred dimension of 0.7 mm; arib A upper cap thickness (dimension “F”) having a broad range of from0.4 mm to 1 mm, a preferred range of from 0.5 mm to 0.8 mm, and apreferred dimension of 0.7 mm; and a rib A central core thickness(dimension “E”) having a broad range of from 0.4 mm to 1 mm, a preferredrange of from 0.5 mm to 0.8 mm, and a preferred dimension of 0.6 mm.

FIG. 12 is a top perspective view of a three-layer polymer startingsheet 1300 having holes formed therein for forming the hexagonalthree-layer integral geogrid 1100 having two outer cellular layers shownin FIGS. 10 and 11 . The three-layer polymer starting sheet 1300includes, disposed between a first expansion outer layer 1310 and asecond expansion outer layer 1330, a third layer, i.e., a non-cellularinner layer 1320.

And, as with the triangular and rectangular geometry embodiments of themultilayer integral geogrid having one or more cellular layers, thehexagonal embodiment of the multilayer integral geogrid 1100 having oneor more cellular layers has a cellular layer that is either foamed orcontains a particulate filler. And, the starting sheet of the hexagonalembodiment of the multilayer integral geogrid having one or morecellular layers is the same as previously disclosed herein for thetriangular and rectangular geometry embodiments, and may be formed bycoextrusion or lamination.

The multilayer polymer starting sheet 1300 used as the starting materialfor a hexagonal multilayer integral geogrid 1100 having one or morecellular layers according to the present invention is preferablythrough-punched, although it may be possible to use depressions formedtherein instead. According to the embodiment of the starting material inwhich depressions are formed in the sheet, the depressions are providedon each side of the sheet, i.e., on both the top and the bottom of thesheet.

As shown in FIG. 12 , the three-layer polymer starting sheet 1300includes a repeating pattern 1310 of holes 1320 and spacing 1330 thatwhen oriented provide the floating hexagon within a hexagon pattern ofthe hexagonal expanded three-layer integral geogrid 1100 shown in FIGS.10 and 11 .

More specifically, a preferred hexagonal three-layer integral geogridaccording to the present invention is as shown in FIG. 38 , which alsoillustrates the continuous strands (or “ribs”) associated with the leftmachine direction (“MD Left”), the right machine direction (“MD Right”),and the transverse direction (“TD”). As shown in FIG. 38 , the “acrossthe flats” (sometimes designated herein as “A/F”) dimension of the outerhexagon repeating unit of the hexagonal embodiment of the integralgeogrid according to the present invention is the distance between theparallel strong axis strands of the outer hexagon, i.e., the strong axisstrands extending parallel to one another in each of the left machinedirection, the right machine direction, and the transverse direction.Even more specifically, per the depiction of the hexagonal embodiment ofthe invention shown in FIGS. 10, 11, and 38 , the A/F dimension is thedistance between any of the parallel strands 1120, i.e., in each of theleft machine direction, the right machine direction, and the transversedirection. According to one preferred embodiment of the hexagonalthree-layer integral geogrid shown in FIG. 38 , the A/F dimension, i.e.,the distance from one multilayer junction 1115 associated with a strand1120 of the outer hexagon (see also FIGS. 10 and 11 ) to the oppositemultilayer junction 1115 associated with a parallel strand 1120 of theouter hexagon, is approximately 80 mm. And, for the same embodiment, theacross the flats dimension, i.e., the distance from one multilayertri-node 1135 of the inner hexagon (see FIG. 11 ) to the oppositemultilayer tri-node 1135 of the inner hexagon, is approximately 33 mm.For this preferred embodiment of the multilayer integral geogridaccording to the present invention, the total starting sheet thicknesshas a broad range of from 2 mm to 12 mm, a preferred range of from 4 mmto 8 mm, and a preferred dimension of 5.5 mm. The punch size/diameterhas a broad range of from 2 mm to 7 mm, a preferred range of from 3 mmto 5 mm, and a preferred dimension of 3.68 mm. The major pitch in thefirst stretch direction has a broad range of from 5 mm to 9 mm, apreferred range of from 6 mm to 8 mm, and preferred dimension of 6.7088mm. The minor pitch in the first stretch direction has a broad range offrom 1 mm to 4 mm, a preferred range of from 2 mm to 3 mm, and apreferred dimension of 2.58 mm. The second major/minor pitch in thefirst stretch direction has a broad range of from 4 mm to 8 mm, apreferred range of from 5 mm to 7 mm, and a preferred dimension of 5.934mm. The major pitch in the second stretch direction has a broad range offrom 4 mm to 8 mm, a preferred range of from 5 mm to 7 mm, and apreferred dimension of 6.192 mm.

And, in general, the three-layer polymer starting sheet 1300 ispolymeric in nature. For example, the material of construction mayinclude high molecular weight polyolefins, and broad specificationpolymers. Furthermore, the polymeric materials may be virgin stock, ormay be recycled materials, such as, for example, post-industrial orpost-consumer recycled polymeric materials. And, the use of one or morepolymeric layers having a lower cost than that of the aforementionedhigh molecular weight polyolefins and broad specification polymers isalso contemplated. According to the preferred embodiment of theinvention, the high molecular weight polyolefin is a polypropylene.

According to a preferred embodiment of the present invention, themultilayer strands 1120, 1140, 1145, 1150, and 1160 of the hexagonalthree-layer integral geogrid 1100 have what is known to one skilled inthe art as a high aspect ratio, i.e., a ratio of the thickness or heightof the multilayer strand cross section to the width of the multilayerstrand cross section that is greater than 1.0 in accordance with theaforesaid Walsh patents, i.e., U.S. Pat. Nos. 9,556,580, 10,024,002, and10,501,896. While not absolutely necessary for the present invention, ahigh aspect ratio for the strands or ribs is preferred. Thus, themulti-axial integral geogrid of the present invention provides enhancedcompatibility between geogrid and aggregate, which results in improvedinterlock, lateral restraint, and confinement of the aggregate.

As noted herein, instead of having the above-described embodiments withthree or more layers, a multilayer integral geogrid having one or morecellular layers according to the present invention may have anon-cellular layer associated with a single adjacent cellular layer.That is, as shown in FIG. 13 , a hexagonal two-layer integral geogrid1500 in accordance with the present invention has one cellular layer1510 and one non-cellular layer 1520. The remaining elements of thehexagonal two-layer integral geogrid 1500 are as described above, exceptthat the multilayer structure has only the two layers, i.e., thecellular layer 1510 and the non-cellular layer 1520.

As shown in FIG. 14 , the two-layer polymer starting sheet 1700associated with the two-layer integral geogrid embodiment of theinvention includes an expansion layer 1710 and a non-cellular layer1720. The expansion layer 1710 and the non-cellular layer 1720 arepreferably arranged in a uniplanar or substantially uniplanarconfiguration. FIG. 15 is a top perspective plan view of a two-layerpolymer starting sheet 1900 that has a pattern of holes 1940 punchedtherein for forming the hexagonal two-layer integral geogrid 1500 shownin FIG. 13 .

More specifically, per FIG. 13 , the hexagonal two-layer integralgeogrid 1500 having one cellular layer includes a repeating pattern offloating inner hexagons 1530 within each outer hexagon 1510. The outerhexagon 1510 includes a plurality of outer oriented multilayer strandsor ribs 1520 interconnected by partially oriented multilayer junctions1515. The inner hexagon 1530 includes a plurality of oriented multilayerconnecting strands 1545 and 1550 interconnected by multilayer tri-nodes1535, and defines a hexagon-shaped center opening 1570. The outerhexagon 1510 is connected to the smaller inner hexagon 1530 by aplurality of multilayer supporting strands 1540 and 1560, which define aplurality of trapezoid-shaped openings 1580. At the center of eachpattern of three adjacent outer hexagons 1510 is a triangular shapedopening 1590. As shown, junctions 1515 are much larger than tri-nodes1535.

The present invention also relates to methods of making theabove-described various embodiments of the multilayer integral geogridshaving one or more cellular layers.

More specifically, it is an object of the present invention to provide amethod of making multilayer integral geogrids having one or morecellular layers in which the layer with the cellular structure isproduced by first providing a foamed construction, i.e., a plurality ofthe cellular openings in a layer of the multilayer polymer startingsheet, and then biaxially orienting the multilayer polymer startingsheet so as to stretch the foamed material and create a distribution ofdeformed cellular openings of the foamed material.

Correspondingly, it is another object of the present invention toprovide a method of making multilayer integral geogrids having one ormore cellular layers in which each layer with the cellular structure isproduced by first dispersing a particulate filler in a layer of themultilayer polymer starting sheet, and then biaxially orienting themultilayer polymer starting sheet so as to stretch the dispersion ofparticulate filler and create a distribution of cellular openings as theparticulate filler partially separates from the polymeric layermaterial.

For example, the method of making the above-described triaxialmultilayer integral geogrid 200 having one or more cellular layersincludes: providing the multilayer polymer starting sheet 100; forming aplurality of holes or depressions in the multilayer polymer startingsheet 100 in a selected pattern, such as in accordance with thedisclosure of the Walsh '112 patent; and biaxially stretching andorienting the multilayer polymer starting sheet having the patternedplurality of holes or depressions therein to form a multilayer integralgeogrid having one or more cellular layers and having a plurality ofinterconnected, oriented multilayer strands between partially orientedmultilayer junctions and to configure the holes or depressions as gridopenings.

In general, once the multilayer polymer starting sheet 100 has beenprepared with holes or depressions, the triaxial multilayer integralgeogrid 200 having one or more cellular layers can be produced from thesheet 100 according to the methods described in the above-identifiedpatents and known to those skilled in the art.

Furthermore, with regard to the method of making the multiaxial“repeating floating hexagon within a hexagon pattern” embodiment of themultilayer integral geogrid having one or more cellular layers, themethod includes providing a polymer sheet 1300; providing a patternedplurality of holes or depressions 1310 in the polymer sheet 1300; andorienting the polymer sheet 1300 having the patterned plurality of holesor depressions 1310 therein to provide a plurality of interconnected,oriented multilayer strands 1120, 1140, 1145, 1150, and 1160 having anarray of openings 1170, 1180, and 1190 therein, a repeating floatinghexagon 1130 within an outer hexagon 1110 pattern of the interconnected,oriented multilayer strands and the openings, including three linearmultilayer strands that extend continuously throughout the entirety ofthe multi-axial multilayer integral geogrid having a layer or layerswith a cellular structure 1100.

In general, once the starting sheet 1300 has been prepared with holes ordepressions, the multi-axial multilayer integral geogrid 1100 having oneor more cellular layers can be produced from the starting sheet 1300according to the methods described in the above-identified patents andknown to those skilled in the art.

With regard to laminating the layers of the multilayer integral geogridinstead of using coextrusion, an approximation of coextruding can beobtained by one of the following methods, although the resulting productin all likelihood will not have all the advantages associated with thepreferred coextruded embodiment. First, separate layers of individuallycast starting sheet can be extruded as individual mono-layers, eachlayer having the required extrusion material recipe. In a post-extrusionprocess, these layers can then be joined into an approximation of anintegrally cast co-extruded material by one of the following processes.For example, a gluing/bonding process can be employed whereby a suitableadhesive is applied to the surfaces of the sheets to be bonded together,e.g., by a padding roller process, and the sheets are then forcedtogether under suitable pressure and or heat to generate a bond. Inanother approach, a heating/laminating process can be employed whereby asuitable heat source is applied to the surfaces of the sheets to bebonded together, e.g., by an induction heated roller or a gas, and thesheets are then forced together under suitable pressure and or heat togenerate a bond. In still another approach, a mechanical welding/bondingprocess can be employed whereby continuous localized welding isperformed by, e.g., ultrasonic or friction welding. And, in stillanother approach, chemical welding/bonding process can be employedwhereby a suitable solvent is introduced to the surfaces of the sheetsto be bonded together, e.g., by a padding roller process, and the sheetsare then forced together under suitable pressure and or heat to generatea bond.

As indicated above, the hexagonal geometric shape of the outer hexagon1110 and smaller inner hexagon 1130 are a preferred embodiment forproviding the floating geometric configuration of the present invention.However, other geometric shapes are possible within the scope of thepresent invention. For example, the geometric shapes could berectangular or square with four supporting or connecting strandsconnecting each inner corner of the outer rectangle or square to thecorresponding outer corner of the smaller inner rectangle or square. Or,the geometric shapes could be triangular with only three supporting orconnecting strands between adjacent inner corners of the outer triangleand outer corners of the smaller inner triangle.

In the rectangular or square embodiment of the present invention,described in the preceding paragraph, there would preferably be twolinear strands that extend continuously throughout the entirety of thegeogrid for each outer rectangle or square, such continuous strandsextending at an angle of approximately 90° from each other. In thetriangular embodiment, there will likely be three linear strands foreach outer triangle which extend from each other by approximately 120°,similar to linear strands 1120 of the preferred hexagon embodimentdescribed in detail herein.

Also, different geometric shapes could be possible without departingfrom the present invention. For example, the inner geometric shape couldbe a circular ring supported within the preferred outer hexagon shapewith six supporting strands similar to the preferred embodimentdisclosed herein. Thus, it is intended that the geometric shapes of theouter repeating structure and the inner or interior floating structurenot be limited to identical geometric forms.

FIGS. 17A-17E illustrate a compression mechanism hypothesis of athree-layer integral geogrid having one or more cellular layersaccording to the present invention that is associated with cellularopenings in the first cellular outer layer 1710 and the second cellularouter layer 1730 under an applied load. As shown in FIG. 17A, prior toan applied loading, the cellular openings 1750 and the polymer 1740around it are undisturbed. As the loading begins (FIG. 17B), the polymer1740 around the cellular openings 1750 begins to compress. As loadingcontinues (FIG. 17C), the polymer 1740 around the cellular openings 1750stops yielding, and the cellular openings 1750 begin to compress. Asmore loading continues (FIG. 17D), the cellular openings 1750 are evenmore compressed and the polymer 1740 around the cellular openings beginsto yield again. And finally, as shown in FIG. 17E, as the loading isremoved, the rib of the expanded multilayer integral geogrid isdecompressed, with permanent cellular opening deformation remaining dueto the cellular openings 1750 having collapsed to a certain degree,along with permanent deformation of the polymer 1740 around the cellularopenings.

FIGS. 18A-18C illustrate a pliable rib mechanism hypothesis of theexpanded, cellular layers of a three-layer integral geogrid having oneor more cellular layers. The pliable rib mechanism hypothesis is alsoassociated with the presence of cellular openings in the first cellularouter layer 1810 and the second cellular outer layer 1830, anddemonstrates both vertical and horizontal pliability of the integralgeogrid under applied load. As shown in FIG. 18A, prior to an appliedloading, the cellular openings 1850 and the polymer 1840 around thecellular openings 1850 are undisturbed. As a load is applied (FIG. 18B),the system begins to undergo elastic compression as the cellularopenings 1850 begin to deform. Finally, as shown in FIG. 18C, the systemstops yielding as the cellular openings 1850 begin to compress anddensify. Thus, by virtue of the cellular openings 1850 present in thefirst cellular outer layer 1810 and the second cellular outer layer 1830of the three-layer integral geogrid, both vertical and horizontalpliability of the integral geogrid under load is achieved.

FIG. 19 presents graphs illustrating a comparison of the non-elastic ribbehavior based on a starting sheet of a conventional integral geogrid,with the elastic rib behavior of a starting sheet of the presentmultilayer integral geogrid having one or more cellular layers. As isevident, ribs of the multilayer integral geogrid having one or morecellular layers that are vertically and horizontally pliable facilitatemore optimum aggregate positioning and densification. This feature ofthe expanded multilayer integral geogrid enables using “big” ribswithout the ribs being “disrupters” of the aggregate system.

Now, turning to additional experimental results that demonstrate theperformance benefits of the present invention, see FIGS. 25, 26, and 27. FIG. 25 illustrates, for a hexagonal three-layer integral geogridaccording to the present invention similar to that shown in FIGS. 10 and11 , the effect of increased rib height on surface deformation during atracking test. The only variation in each of the three specimensassociated with FIG. 25 is the thickness of the starting sheet, which,of course, determines the resulting rib height of the integral geogrid.FIG. 26 is a plot of the effect of increased rib height on surfacedeformation associated with the test results presented in FIG. 25 . And,FIG. 27 is a table summarizing the effect of increased rib height onsurface deformation associated with the test results presented in FIGS.25 and 26 . As is evident from the trafficking test results shown inFIGS. 25, 26, and 27 , as rib height increases, the surface deformationof the integral geogrid advantageously decreases.

Furthermore, the integral geogrid having the layers with the cellularstructure according to the present invention has other advantageouscharacteristics. FIG. 28 is a plot of the increased rib heightachievable with a hexagonal three-layer integral geogrid according tothe present invention versus that achievable with a solid monolayergeogrid. And, for the same integral geogrids as are associated with theFIG. 28 results, FIG. 29 is a plot of the reduced mass per unit areaachievable with a hexagonal three-layer integral geogrid according tothe present invention versus that achievable with a solid monolayergeogrid. As is evident from FIGS. 28 and 29 , the integral geogridhaving the outer “cap” layers with the cellular structure according tothe present invention has an average rib height of more than 10% of thatwhich is achievable with a solid monolayer geogrid, while also having aunit weight that is 11% less than that of the solid monolayer geogrid.

Now, turning to additional experimental trafficking results thatdemonstrate the performance benefits of the present invention, see FIGS.30 and 31 . FIG. 30 is a plot of the improved performance achievablewith a hexagonal three-layer integral geogrid having compressible,cellular outer layers according to the present invention versus thatachievable with a hexagonal solid monolayer geogrid. FIG. 31 is a tablesummarizing the structural data associated with the hexagonalthree-layer integral geogrid having compressible, cellular outer layersand the hexagonal solid monolayer geogrid utilized in the test resultspresented in FIG. 30 . The starting sheets associated with each specimenhave a thickness of 6.2 mm for the three-layer integral geogrid havingcompressible, cellular outer layers, and 6.3 mm for the solid monolayergeogrid. As is evident from the trafficking test results shown in FIGS.30 and 31 , the three-layer integral geogrid having compressible,cellular outer layers advantageously has less surface deformation thanof the solid monolayer geogrid. In fact, in terms of the number oftrafficking test passes for limiting deformation, the presentinvention's three-layer integral geogrid having compressible, cellularouter layers is approximately 9 times better than the solid monolayergeogrid.

Similarly, FIGS. 32 and 33 present experimental trafficking results thatdemonstrate the performance benefits of the present invention. FIG. 32is another plot of the improved performance achievable with a hexagonalthree-layer integral geogrid having compressible, cellular outer layersaccording to the present invention versus that achievable with ahexagonal solid monolayer geogrid. FIG. 33 is a table summarizing thestructural data associated with the hexagonal three-layer integralgeogrid having compressible, cellular outer layers and the hexagonalsolid monolayer geogrid utilized in the test results presented in FIG.32 . The starting sheets associated with each specimen in the FIGS. 32and 33 results are thicker, with a thickness of 7.5 mm for thethree-layer integral geogrid having compressible, cellular outer layers,and 7.5 mm for the solid monolayer geogrid. As is evident from thetrafficking test results shown in FIGS. 32 and 33 , the three-layerintegral geogrid having compressible, cellular outer layersadvantageously has less surface deformation than of the solid monolayergeogrid. In fact, in terms of the number of trafficking test passes forlimiting deformation, the present invention's three-layer integralgeogrid having compressible, cellular outer layers is approximately 5times better than the solid monolayer geogrid.

Now, turning to the compressibility of the inventive integral geogrid,FIG. 34 is a plot of the improved compressibility achievable with ahexagonal three-layer integral geogrid having compressible, cellularouter layers according to the present invention versus that achievablewith a hexagonal solid monolayer geogrid. And, FIG. 35 is a tablesummarizing the force required to produce a certain compressibilityassociated with the hexagonal three-layer integral geogrid havingcompressible, cellular outer layers according to the present inventionand the hexagonal solid monolayer geogrid utilized in the test resultspresented in FIG. 34 . The results shown in FIGS. 34 and 35 demonstratethat the three-layer integral geogrid having compressible, cellularouter layers according to the present invention requires significantlyless force to compress than a solid monolayer geogrid. Morespecifically, the three-layer integral geogrid having compressible,cellular outer layers according to the present invention requiresbetween 12% and 54% of the amount of force to compress than the solidmonolayer geogrid.

And now, FIGS. 36 and 37 present stress—strain experimental results thatdemonstrate the performance benefits of the present invention. FIG. 36is a plot of the stiffness achievable with a hexagonal three-layerintegral geogrid having compressible, cellular outer layers according tothe present invention versus that achievable with a hexagonal solidmonolayer geogrid. FIG. 37 is a table summarizing the stress and strainassociated with the hexagonal three-layer integral geogrid havingcompressible, cellular outer layers and the hexagonal solid monolayergeogrid utilized in the test results presented in FIG. 36 . Grids A andC are specimens having the three-layer compressible cellular outer layerstructure according to the present invention. Grid E is a specimenhaving a solid monolayer structure. As is evident from FIGS. 36 and 37 ,for the three-layer compressible cellular outer layer structureaccording to the present invention, there is no loss in either stiffnessor strength.

Now, turning to additional compressibility comparisons, FIG. 41 shows anexperimental apparatus used to measure the compressibility of anintegral geogrid 1100 specimen. The apparatus employs a 1.6 mm widemetal probe 1910 and the application of a 125 N force to compress theintegral geogrid 1100 specimens. As shown in FIG. 42 , thecompressibility of the integral geogrid specimens having a layer with acellular structure according to the present invention, i.e., NX750,NX850, and NX950, is substantially greater than that of the specimensnot having a layer with a cellular structure, i.e., TX160 and HexagonalMono.

And, as shown in FIG. 43 , both the compressibility and the reboundability of the integral geogrid specimens having a layer with a cellularstructure according to the present invention, i.e., Hexagonal UK 7.5 mm,NX750, NX850, Hexagonal UK 5.45 mm, NGA 4.5 mm, and NGB 5 mm, issubstantially greater than that of the specimens not having a layer witha cellular structure, i.e., TX5, TX7, BX 1200 MD, BX1100 MD, BX1100 TD,TX160, and BX1200 TD.

FIG. 44 shows another experimental apparatus associated with determiningcompressibility, a Plate Load Test Rig (“PLTR”), used to measure thedisplacement of an integral geogrid specimen. In the test, an integralgeogrid specimen is layered between a 4-inch layer of aggregate and alayer of foam, with a steel plate being located beneath the foam layer.To determine the compressibility of an integral geogrid specimen, a1,000 lb force is imparted over 10 cycles to the aggregate/integralgeogrid/foam stack. The integral geogrid specimen is then removed fromthe apparatus and examined for rib compressibility and surface damage.

From the tests using the apparatus shown in FIG. 44 , the averagedisplacement of various integral geogrid specimens when employing a softfoam and a hard foam is shown, respectively, in FIG. 45 and FIG. 46 . Asto the meaning of the terms “soft foam” and “hard foam” as used in theaforementioned tests, FIGS. 58 and 59 , respectively, present graphsillustrating compression force versus displacement data for such softand hard foam embodiments. To generate the data shown in FIGS. 58 and 59, an apparatus having a square metal plate, measuring 3 inches×3 inches,is connected via a swivel joint capable of accommodating the angle ofthe sample to a force-measuring device (such as, for example, an Instrontesting machine), and mounted in such a manner that the foam specimencan be compressed at a speed of 10 mm/minute. The apparatus is arrangedto support the specimen on a level horizontal plate.

As is evident from FIGS. 45 and 46 , the displacement of the integralgeogrid specimens having a layer with a cellular structure according tothe present invention, i.e., NX750, NX850, NGA, and NGB, isadvantageously less than that of the specimens not having a layer with acellular structure, i.e., TX5, TX160, and TX7.

And now, turning to trafficking test results, FIGS. 47-57 presentexperimental data that reflect various integral geogrid structuralfeatures and parameters that can impact the structural deformation of anintegral geogrid when in use. FIGS. 47-51 and the associated descriptionof each are presented herein simply as background information, i.e., asa way of describing how the research and development efforts of theinventors led to the integral geogrid structures described herein as theembodiments of the invention. The experimental data associated with saidembodiments of the invention are presented in FIGS. 52-57 .

With regard to the background information, FIG. 47 provides a comparisonof the effect of compressibility on the relationship between rib aspectratio and surface deformation for two integral geogrids, i.e., amonolayer integral geogrid and a coextruded multilayer integral geogridwith one layer having a cellular structure. FIG. 47 shows that, duringtrafficking, directionally at least, an integral geogrid having acoextruded multilayer structure with some degree of compressibility hassome benefit in terms of the relationship between surface deformationand rib aspect ratio. That is, with a coextruded multilayer structurehaving some degree of compressibility, obtaining lower surfacedeformation without resorting to a very high aspect ratio can bebeneficial.

However, turning to FIG. 48 , another comparison of the effect ofcompressibility on the relationship between rib aspect ratio and surfacedeformation for two integral geogrids i.e., a monolayer integral geogridand a coextruded multilayer integral geogrid with one layer having acellular structure, shows that the benefit shown in FIG. 47 can,depending upon the integral geogrid geometry, be less pronounced. Whilethe integral geogrids employed in the FIG. 47 test have a 66 mm acrossthe flats dimension, the integral geogrids employed in the FIG. 48 testhave an 80 mm across the flats dimension. Essentially, the FIG. 48 datashow that some benefit can be derived from optimizing both materialproperties and geometry, as an 80 mm geometry is, in general, moresuitable than a 66 mm geometry for the majority of granular materialsencountered in typical geogrid applications.

Now, turning to a comparison based on geometry alone, FIG. 49 shows theeffect of base geometry on the ability of rib aspect ratio to influencesurface deformation for two integral geogrids not having a layer with acellular structure, i.e., a triaxial integral geogrid, and a hexagonalintegral geogrid as described herein. FIG. 49 shows that, duringtrafficking, directionally at least, an integral geogrid having ahexagonal geometry has some benefit in terms of the relationship betweensurface deformation and rib aspect ratio. That is, with a hexagonalgeometry, obtaining lower surface deformation without resorting to avery high aspect ratio can be beneficial. And finally, with regard tothe background information, FIG. 50 provides a comparison of thebenefits of base geometry in similarly compressible integral geogridproducts. That is, FIG. 50 shows that, during trafficking, for atriaxial integral geogrid and a hexagonal integral geogrid, each ofwhich has a single inner layer having a cellular structure disposedbetween a first and a second outer layer of a non-cellular structure,use of the hexagonal geometry is beneficial in that it provides lowersurface deformation with a lower rib aspect ratio. Similarly, FIG. 51provides graphically a comparison of the effect of base geometry on therelationship between rib aspect ratio and surface deformation insimilarly compressible integral geogrids, i.e., the above-describedtriaxial integral geogrid and hexagonal integral geogrid.

Now, turning to the trafficking data associated with the variousembodiments of the instant invention, the experimental results shown inFIGS. 52-57 demonstrate the benefit to be achieved with an integralgeogrid having first and second outer layers of a cellular structure asdescribed herein, and an inner layer of a non-cellular structure.

FIG. 52 provides a comparison, for a single base geometry, of the effecton surface deformation of the position of the layer with a cellularstructure in the multilayered integral geogrid. FIG. 53 provides agraphical comparison, for the single base geometry associated with FIG.52 , of the effect of the position of the layer with a cellularstructure on the relationship between rib aspect ratio and surfacedeformation. As is evident from FIGS. 52 and 53 , the integral geogridaccording to the present invention having the outer layers of a cellularstructure and an inner layer of a non-cellular structure exhibits lesssurface deformation during trafficking than an integral geogrid havingthe cellular structure layer as the inner layer.

And, FIG. 54 provides still another comparison for the single basegeometry associated with FIG. 52 , of the effect on surface deformationof the position of the layer with a cellular structure in themultilayered integral geogrid. The associated FIG. 55 presents anothergraphical comparison, for the single base geometry associated with FIG.52 , of the effect of the position of the layer with a cellularstructure on the relationship between rib aspect ratio and surfacedeformation. In the experiments reported in FIGS. 54 and 55 , theperformance of a three-layer integral geogrid having outer cellularstructure layers is compared with both a five-layer integral geogridhaving two “sandwiched” inner cellular structure layers, and an integralgeogrid having a single layer without a cellular structure. As isevident from FIGS. 54 and 55 , of the three aforementioned integralgeogrid structures, the integral geogrid according to the presentinvention having the outer layers of a cellular structure and an innerlayer of a non-cellular structure exhibits the least surface deformationduring trafficking.

And finally, FIGS. 56 and 57 present experimental data that reflect thecombined beneficial effect of incorporating in an integral geogrid thevarious features of the integral geogrid according to the presentinvention. FIG. 56 provides a comparison, for the integral geogridaccording to the present invention having the single base geometryassociated with FIG. 52 and a prior art geogrid not having a layer witha cellular structure, of the effect on surface deformation of the layerwith a cellular structure. And, the associated FIG. 57 provides agraphical comparison, for the integral geogrid according to the presentinvention having the single base geometry associated with FIG. 52 and aprior art geogrid not having a layer with a cellular structure, of theeffect of the compressibility of the layer with a cellular structure onthe relationship between rib aspect ratio and surface deformation. FIGS.56 and 57 show that by optimizing both the geometry and the materialproperties via coextrusion, and by correctly positioning the layershaving the compressive, cellular structure, the integral geogridaccording to the present invention provides a reduction of approximately25% in terms of aggregate surface deformation. Furthermore, theaforementioned result is achieved with starting sheet thicknesses thatare between 12% and 28% of those of prior art geogrids.

In summary, by virtue of the multilayer integral geogrids having one ormore cellular layers of the present invention having not only amultilayer construction, but with at least one layer thereof having acellular structure as a result of the distribution of cellular openingstherein, the integral geogrids provide for increased layercompressibility under load.

Furthermore, the multilayer nature of the multilayer integral geogridshaving one or more cellular layers of the present invention provides foroverall greater aggregate engagement by the integral geogrid relative tothat of prior monolayer integral geogrids. In addition, by virtue of theone or more cellular layers, the multilayer integral geogrids of thepresent invention are characterized by a structural compliance, i.e.,initial give or flexibility, that leads to better compaction and higherdensity, yet with a final integral geogrid composite stiffness whenincorporated in a soil construction that is greater as a result of theinitial give of the multilayer integral geogrid.

In addition, certain embodiments of the multilayer integral geogridshaving one or more cellular layers of the present invention providehigher aspect ratios on all strands compared to those of prior integralgeogrids. Because the higher aspect ratio associated with certainembodiments of the integral geogrids of the present invention increasesaggregate interlock, the multilayer integral geogrids having one or morecellular layers of the present invention can better accommodate thevarying aspect ratios of aggregate.

The foregoing is considered as illustrative only of the principles ofthe invention. Furthermore, since numerous modifications and changes mayreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation described andshown.

What is claimed is:
 1. A multilayer integral geogrid for interlockingwith, stabilizing, and strengthening aggregate, said integral geogridcomprising: a plurality of layers each of a polymeric material, with atleast a first outer layer and a second outer layer of said plurality oflayers having a cellular structure to improve the initial interactionbetween and compatibility of a soil or aggregate and the integralgeogrid to maximize soil or aggregate density and properties aftercompaction, and wherein each of the polymeric layers comprises aplurality of interconnected oriented strands and partially orientedjunctions forming a repeating pattern of outer hexagons having an arrayof openings therein, supporting ribs extending inwardly from each ofsaid outer hexagons to support inside each of said outer hexagons asmaller inner hexagon having an unobstructed, open center and orientedstrands and tri-nodes, each of said tri-nodes interconnecting only oneof said supporting ribs and two of said oriented strands of the innerhexagon, said outer hexagons, said supporting ribs and said innerhexagons defining three different geometric configurations which arerepeating throughout an entirety of the integral geogrid, and saidoriented strands and said partially oriented junctions of said outerhexagons defining a plurality of linear strands that extend continuouslythroughout the entirety of the integral geogrid.
 2. The multilayerintegral geogrid according to claim 1, wherein the first cellular outerlayer and the second cellular outer layer have a void volume of fromabout 20% to about 70%.
 3. The multilayer integral geogrid according toclaim 1, wherein the first cellular outer layer and the second cellularouter layer have a compressibility factor of from about 20% to about60%.
 4. The multilayer integral geogrid according to claim 1, whereinthe first cellular outer layer and the second cellular outer layer havea foam construction.
 5. The multilayer integral geogrid according toclaim 4, wherein the foam is associated with a foaming agent or gasinjection.
 6. The multilayer integral geogrid according to claim 1,wherein the first cellular outer layer and the second cellular outerlayer have a construction that includes a particulate filler.
 7. Themultilayer integral geogrid according to claim 6, wherein theparticulate filler is calcium carbonate.
 8. The multilayer integralgeogrid according to claim 1, wherein the multilayer integral geogrid isproduced from a coextruded multilayer polymer sheet.
 9. The multilayerintegral geogrid according to claim 1, wherein the multilayer integralgeogrid is produced from a laminated multilayer polymer sheet.
 10. Themultilayer integral geogrid according to claim 1, wherein the orientedstrands have been biaxially stretched.
 11. The multilayer integralgeogrid according to claim 1, wherein the multilayer integral geogridhas the first cellular outer layer, a non-cellular inner layer, and thesecond cellular outer layer, with the first cellular outer layer and thesecond cellular outer layer being arranged on opposite planar surfacesof the non-cellular inner layer.